SAN Switch Migration - How to plan and what need to consider?

       The Zoning Migration within SAN Fabric can import complete zone set information and aliases without any effect on existing SAN fabrics, simplifying SAN migration between different vendors. Such as Cisco, Brocade and McData.

         Import of zone set(h/w + s/w) actually save up a lot time for the migration work but there is some preparation need to be done before the migration. Prepare of the script of zone set, check the interopmode for future fabric expansion (In case other brand of switch will be add in the fabric is required)

     Before you begin, save the current Production Fabric from all SAN Switches.

           Example of Import Zone set. Export the zoning info from the Old switches and prepare the script and import to the new SAN. One important reminder, make sure you have configured the Interoperation mode “Interopmode” before you import the zone set. As the change of Interopmode setting will reset the zoning config.  Make sure all Switch that going to merge / ISL are in the same or Compatible Interop-Mode.

Before ISL / merge the switches,  you need to make sure all Switch in the fabric have a unique DID. You need to determine the principal switch in the fabric. This is to ensure that you have a proper fabric management  for future expansion.

Migration between Brocade Switches is very Simple and easy. Below is the script that I prepared before I import to the new Brocade switch.

Create Zone

switch>zonecreate "USUNIXSAN_HBA0_CX1234_SPA0","10:00:00:00:C9:2D:10:12;50:06:01:60:39:01:2D:xx"

switch>zonecreate "USUNIXSAN_HBA0_CX1234_SPB0","10:00:00:00:C9:23:11:13;50:06:01:68:39:01:2D:xx"

switch>zonecreate "SANDUEL_HBA0_CX1234_SPA0","10:00:00:00:C9:2A:10:17;50:06:01:60:39:01:2D:xx"

switch>zonecreate "SANDUEL_HBA0_CX1234_SPB0","10:00:00:00:C9:23:12:3D;50:06:01:68:39:01:2D:xx"

switch>zonecreate "WINAPPS2008_HBA0_CX1234_SPA0","10:00:00:00:C9:2D:10:12;50:06:01:60:39:01:2D:xx"

switch>zonecreate "WINAPPS2008_HBA0_CX1234_SPB0","10:00:00:00:C9:23:11:13;50:06:01:68:39:01:2D:xx"

---

Config Create

switch>cfgcreate "SANDUEL_FabricA", "USUNIXSAN_HBA0_CX1234_SPA0"

switch>cfgadd "SANDUEL_FabricA", "USUNIXSAN_HBA0_CX1234_SPB0"

switch>cfgadd "SANDUEL_FabricA", "SANDUEL_HBA0_CX1234_SPA0"

switch>cfgadd "SANDUEL_FabricA", "SANDUEL_HBA0_CX1234_SPB0"

switch>cfgadd "SANDUEL_FabricA", "WINAPPS2008_HBA0_CX1234_SPA0"

switch>cfgadd "SANDUEL_FabricA", "WINAPPS2008_HBA0_CX1234_SPB0"

---

switch>enable the configure.

switch>cfgenable “SANDUEL_FabricA”

Brocade switch Zoning and Fabric Operations

        When configuring zoning or other fabric-wide settings in a fabric that has products operating with different versions of FOS, it is recommended that the configuration be performed via an interface (such as WebTools) to a product with the most recent version of FOS. 

       Some older versions of FOS do not fully support newer hardware models, and problems may arise when configuring settings through these older products. 

       Zoning configuration in particular should never be performed through a switch operating with FOS v3.x in a fabric that also has products operating with newer releases of FOS firmware.

Brocade Switch Technical Support

Contact your switch supplier for hardware, firmware, and software support, including product repairs and part ordering. To expedite your call, have the following information immediately available :




1. General Information

· Technical Support contract number, if applicable

· Switch model

Fabric OS v6.1.1a Release Notes, v1.0 Page 6 of 33

· Switch operating system version

· Error numbers and messages received


· supportSave command output

· Detailed description of the problem, including the switch or fabric behavior immediately
following the problem, and specific questions

· Description of any troubleshooting steps already performed and the results

· Serial console and Telnet session logs

· Syslog message logs


2. Switch Serial Number

The switch serial number is provided on the serial number label.
 
The serial number label is located as follows:

· Brocade 200E—On the nonport side of the chassis

· Brocade 4100, 4900, and 7500/7500E—On the switch ID pull-out tab located inside the
chassis on the port side on the left

· Brocade 300, 5000, 5100, and 5300—On the switch ID pull-out tab located on the bottom of
the port side of the switch

· Brocade 7600—On the bottom of the chassis

· Brocade 48000 —Inside the chassis next to the power supply bays

· Brocade DCX—Bottom right of the port side.



3. World Wide Name (WWN)

Use the wwn command to display the switch WWN.

If you cannot use the wwn command because the switch is inoperable, you can get the
WWN from the same place as the serial number, except for the Brocade DCX. For the
Brocade DCX, access the numbers on the WWN cards by removing the Brocade logo
plate at the top of the non-port side. The WWN is printed on the LED side of both cards.

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ISCSI Design Considerations

1. General Discussion

Traditionally, storage controllers (e.g., disk array controllers,tape library controllers) have supported the SCSI-3 protocol and have been attached to computers by SCSI parallel bus or Fibre Channel. The IP infrastructure offers compelling advantages for volume/ block-oriented storage attachment. It offers the opportunity to take advantage of the performance/cost benefits provided by competition in the Internet marketplace. This could reduce the cost of storage network infrastructure by providing economies arising from the need to install and operate only a single type of network.

  In addition, the IP protocol suite offers the opportunity for a rich array of management, security and QoS solutions. Organizations may

initially choose to operate storage networks based on iSCSI that are independent of (isolated from) their current data networks except for secure routing of storage management traffic. These organizations anticipated benefits from the high performance/cost of IP equipment and the opportunity for a unified management architecture. As security and QoS evolve, it becomes reasonable to build combined

networks with shared infrastructure; nevertheless, it is likely that sophisticated users will choose to keep their storage sub-networks isolated to afford the best control of security and QoS to ensure a high-performance environment tuned to storage traffic.

   Mapping SCSI over IP also provides:

-- Extended distance ranges

-- Connectivity to "carrier class" services that support IP

   The following applications for iSCSI are contemplated:

-- Local storage access, consolidation, clustering and pooling (as in the data center)

-- Network client access to remote storage (eg. a "storage service provider")

-- Local and remote synchronous and asynchronous mirroring between storage controllers

-- Local and remote backup and recovery

  ISCSI will support the following topologies:

-- Point-to-point direct connections

-- Dedicated storage LAN, consisting of one or more LAN segments

-- Shared LAN, carrying a mix of traditional LAN traffic plus storage traffic

-- LAN-to-WAN extension using IP routers or carrier-provided "IP Datatone"

-- Private networks and the public Internet IP LAN-WAN routers may be used to extend the IP storage network to the wide area, permitting remote disk access (as for a storage utility), synchronous and asynchronous remote mirroring, and remote backup and restore (as for tape vaulting). In the WAN, using TCP end-to-end avoids the need for specialized equipment for protocol conversion, ensures data reliability, copes with network congestion, and provides retransmission strategies adapted to WAN delays.

    The ISCSI technology deployment will involve the following elements:

(1) Conclusion of a complete protocol standard and supporting implementations;

(2) Development of Ethernet storage NICs and related driver and protocol software; 

[NOTE: high-speed applications of iSCSI are expected to require significant portions of the iSCSI/TCP/IP implementation in hardware to achieve the necessary throughput.]

(3) Development of compatible storage controllers; and

(4) The likely development of translating gateways to provide connectivity between the Ethernet storage network and the Fibre Channel and/or parallel-bus SCSI domains.

(5) Development of specifications for iSCSI device management such as MIBs, LDAP or XML schemas, etc.

(6) Development of management and directory service applications to support a robust SAN infrastructure. Products could initially be offered for Gigabit Ethernet attachment,

with rapid migration to 10 GbE. For performance competitive with alternative SCSI transports, it will be necessary to implement the performance path of the full protocol stack in hardware. These new storage NICs might perform full-stack processing of a complete SCSI

task, analogous to today's SCSI and Fibre Channel HBAs, and might also support all host protocols that use TCP (NFS, CIFS, HTTP, etc).

   The charter of the IETF IP Storage Working Group (IPSWG) describes the broad goal of mapping SCSI to IP using a transport that has

proven congestion avoidance behavior and broad implementation on a variety of platforms. Within that broad charter, several transport

alternatives may be considered. Initial IPS work focuses on TCP, and this requirements document is restricted to that domain of interest.

2. Performance/Cost

   In general, iSCSI MUST allow implementations to equal or improve on the current state of the art for SCSI interconnects. This goal breaks down into several types of requirement:

Cost competitive with alternative storage network technologies:

In order to be adopted by vendors and the user community, the iSCSI protocol MUST enable cost competitive implementations when compared

to other SCSI transports (Fibre Channel).

Low delay communication:

Conventional storage access is of a stop-and-wait remote procedure call type. Applications typically employ very little pipelining of their storage accesses, and so storage access delay directly impacts performance. The delay imposed by current storage interconnects,

including protocol processing, is generally in the range of 100 microseconds. The use of caching in storage controllers means that many storage accesses complete almost instantly, and so the delay of the interconnect can have a high relative impact on overall performance. When stop-and-wait IO is used, the delay of the interconnect will affect performance. The iSCSI protocol SHOULD minimize control overhead,  which adds to delay.

Low host CPU utilization, equal to or better than current technology:

For competitive performance, the iSCSI protocol MUST allow three key implementation goals to be realized:

(1) iSCSI MUST make it possible to build I/O adapters that handle an entire SCSI task, as alternative SCSI transport implementations do.

(2) The protocol SHOULD permit direct data placement ("zero-copy" memory architectures, where the I/O adapter reads or writes host memory exactly once per disk transaction.

(3) The protocol SHOULD NOT impose complex operations on the host software, which would increase host instruction path length relative to alternatives.

Direct data placement (zero-copy iSCSI):

   Direct data placement refers to iSCSI data being placed directly "off the wire" into the allocated location in memory with no intermediate copies. Direct data placement significantly reduces the memory bus and I/O bus loading in the endpoint systems, allowing improved performance. It reduces the memory required for NICs, possibly reducing the cost of these solutions.

   This is an important implementation goal. In an iSCSI system, each of the end nodes (for example host computer and storage controller) should have ample memory, but the intervening nodes (NIC, switches) typically will not.

High bandwidth, bandwidth aggregation:

  The bandwidth (transfer rate, MB/sec) supported by storage controllers is rapidly increasing, due to several factors:

1. Increase in disk spindle and controller performance; 

2. Use of ever-larger caches, and improved caching algorithms;

3. Increased scale of storage controllers (number of supported spindles, speed of interconnects).

    The iSCSI protocol MUST provide for full utilization of available link bandwidth. The protocol MUST also allow an implementation to

exploit parallelism (multiple connections) at the device interfaces and within the interconnect fabric.

*****

  The next two sections further discuss the need for direct data placement and high bandwidth.

3. Framing

   Framing refers to the addition of information in a header, or the data stream to allow implementations to locate the boundaries of an iSCSI protocol data unit (PDU) within the TCP byte stream. There are two technical requirements driving framing: interfacing needs, and accelerated processing needs.

  A framing solution that addresses the "interfacing needs" of the iSCSI protocol will facilitate the implementation of a message-based upper layer protocol (iSCSI) on top of an underlying byte streaming protocol (TCP). Since TCP is a reliable transport, this can be

accomplished by including a length field in the iSCSI header. Finding the protocol frame assumes that the receiver will parse from the beginning of the TCP data stream, and never make a mistake (lose alignment on packet headers).

  The other technical requirement for framing, "accelerated processing", stems from the need to handle increasingly higher data rates in the physical media interface. Two needs arise from higher data rates:

(1) LAN environment - NIC vendors seek ways to provide "zero-copy" methods of moving data directly from the wire into application buffers.

(2) WAN environment- the emergence of high bandwidth, high latency, low bit error rate physical media places huge buffer requirements on the physical interface solutions.

     First, vendors are producing network processing hardware that offloads network protocols to hardware solutions to achieve higher data rates. The concept of "zero-copy" seeks to store blocks of data in appropriate memory locations (aligned) directly off the wire, even when data is reordered due to packet loss. This is necessary to drive actual data rates of 10 Gigabit/sec and beyond.

Secondly, in order for iSCSI to be successful in the WAN arena it must be possible to operate efficiently in high bandwidth, high delay

networks. The emergence of multi-gigabit IP networks with latencies in the tens to hundreds of milliseconds presents a challenge. To fill such large pipes, it is necessary to have tens of megabytes of outstanding requests from the application. In addition, some protocols potentially require tens of megabytes at the transport layer to deal with buffering for reassembly of data when packets are received out-of-order.

     In both cases, the issue is the desire to minimize the amount of memory and memory bandwidth required for iSCSI hardware solutions.

  Consider that a network pipe at 10 Gbps x 200 msec holds 250 MB. [Assume land-based communication with a spot half way around the world at the equator. Ignore additional distance due to cable routing. Ignore repeater and switching delays; consider only a speed-of-light delay of 5 microsec/km. The circumference of the globe at the equator is approx. 40000 km (round-trip delay must be considered to keep the pipe full). 10 Gb/sec x 40000 km x 5 microsec/km x B / 8b = 250 MB]. In a conventional TCP implementation, loss of a TCP segment means that stream processing MUST stop until that segment is recovered, which takes at least a time of <network round trip> to accomplish. Following the example above, an implementation would be obliged to catch 250 MB of data into an anonymous buffer before resuming stream processing; later, this data would need to be moved to its proper location. Some proponents of iSCSI seek some means of putting data directly where it belongs, and avoiding extra data movement in the case of segment drop. This is a key concept in understanding the debate behind framing methodologies.

   The framing of the iSCSI protocol impacts both the "interfacing needs" and the "accelerated processing needs", however, while

including a length in a header may suffice for the "interfacing needs", it will not serve the direct data placement needs. The framing mechanism developed should allow resynchronization of packet boundaries even in the case where a packet is temporarily missing in the incoming data stream.

4. High bandwidth, bandwidth aggregation

   At today's block storage transport throughput, any single link can be saturated by the volume of storage traffic. Scientific data

applications and data replication are examples of storage applications that push the limits of throughput.

   Some applications, such as log updates, streaming tape, and replication, require ordering of updates and thus ordering of SCSI

commands. An initiator may maintain ordering by waiting for each update to complete before issuing the next (a.k.a. synchronous updates). However, the throughput of synchronous updates decreases inversely with increases in network distances.

  For greater throughput, the SCSI task queuing mechanism allows an initiator to have multiple commands outstanding at the target simultaneously and to express ordering constraints on the execution of those commands. The task queuing mechanism is only effective if

the commands arrive at the target in the order they were presented to the initiator (FIFO order). The iSCSI standard must provide an

ordered transport of SCSI commands, even when commands are sent along different network paths (see Section 5.2 SCSI). This is referred to

as "command ordering".

    The iSCSI protocol MUST operate over a single TCP connection to accommodate lower cost implementations. To enable higher performance

storage devices, the protocol should specify a means to allow operation over multiple connections while maintaining the behavior of

a single SCSI port. This would allow the initiator and target to use multiple network interfaces and multiple paths through the network for increased throughput. There are a few potential ways to satisfy the multiple path and ordering requirements.

    A popular way to satisfy the multiple-path requirement is to have a driver above the SCSI layer instantiate multiple copies of the SCSI

transport, each communicating to the target along a different path. "Wedge" drivers use this technique today to attain high performance. Unfortunately, wedge drivers must wait for acknowledgement of completion of each request (stop-and-wait) to ensure ordered updates.

Another approach might be for iSCSI protocol to use multiple instances of its underlying transport (e.g. TCP). The iSCSI layer would make these independent transport instances appear as one SCSI transport instance and maintain the ability to do ordered SCSI command queuing. The document will refer to this technique as "connection binding" for convenience.

   The iSCSI protocol SHOULD support connection binding, and it MUST be optional to implement.

 

   In the presence of connection binding, there are two ways to assign features to connections. In the symmetric approach, all the connections are identical from a feature standpoint. In the

asymmetric model, connections have different features. For example, 

  some connections may be used primarily for data transfers whereas others are used primarily for SCSI commands.

  Since the iSCSI protocol must support the case where there was only one transport connection, the protocol must have command, data, and status travel over the same connection.

  In the case of multiple connections, the iSCSI protocol must keep the command and its associated data and status on the same connection (connection allegiance). Sending data and status on the same connection is desirable because this guarantees that status is received after the data (TCP provides ordered delivery). In the case where each connection is managed by a separate processor, allegiance decreases the need for inter-processor communication. This symmetric

approach is a natural extension of the single connection approach. 

  An alternate approach that was extensively discussed involved sending all commands on a single connection and the associated data and

status on a different connection (asymmetric approach). In this scheme, the transport ensures the commands arrive in order. The protocol on the data and status connections is simpler, perhaps lending itself to a simpler realization in hardware. One disadvantage of this approach is that the recovery procedure is

different if a command connection fails vs. a data connection. Some argued that this approach would require greater inter-processor communication when connections are spread across processors.

     The reader may reference the mail archives of the IPS mailing list between June and September of 2000 for extensive discussions on

symmetric vs asymmetric connection models. 

Introduction to ISCSI

      The IP Storage Working group is chartered with developing comprehensive technology to transport block storage data over IP protocols. This effort includes a protocol to transport the Small Computer Systems Interface (SCSI) protocol over the Internet (iSCSI). The initial version of the iSCSI protocol will define a mapping of SCSI transport protocol over TCP/IP so that SCSI storage controllers (principally disk and tape arrays and libraries) can be attached to IP networks, notably Gigabit Ethernet (GbE) and 10 Gigabit Ethernet (10 GbE) the iSCSI protocol is a mapping of SCSI to TCP, and constitutes a "SCSI transport".

How to change IP V4 of the Brocade Switch ( or any server ) to your LAN IP v4:(If it have another LAN IP)

Step1:

      Take the Current ip of the Brocade

      Switch

    Ex: 192.168.5.1

Step2: 
       Find the local Ip series you want to

       give to your machine.
   
    Ex: 192.168.0.1

Step3:
    Take one system and prepare it with ip in the same series of your brocade switch (or server).

 Ex: with ip 192.168.5.2

step4:

      Telnet from your server(192.168.5.2) to the brocade switch (or server(192.168.5.1)).

Ex:
In Brocade Switch
     #ifconfig -a

       ip is 192.168.5.2

     #telnet 192.168.5.1

     switch>ipaddrshow

      ip is 192.168.5.1

     switch>ipaddrset
     one interactive session is opened to take the new ip of the switch , subnetmask and default gateway.then give your ip as 192.168.0.1

     switch>ipaddrshow

      ip is 192.168.0.1

     logout the switch.now switch in the same local network lan.


In solaris server

   ##telnet 192.168.5.1

  telnet into the server as like the telnet in the switch.after

    solaris##ifconfig -a

     It gives the ip of the current solaris server with the interface.
  
syntax: solaris##ifconfig interfacename ipaddress plumb

    Solaris##ifconfig eri0 192.168.0.1 plumb

After plumbing up the interface with the new ip address.

    solaris##ifconfig eri0 192.168.0.1 up

    solaris##ifconfig -a

     ip address is 192.168.0.1

    Task is completed, then logout the server.


step5:


  Also change the your console loggedin server ip to your local LAN series IP.
   

SAN Interview questions part 1

 

  1. WHAT ARE THE BENEFITS OF FIBRE CHANNEL SANS?

          Fibre Channel SANs are the de facto standard for storage networking in the corporate data center because they provide exceptional reliability, scalability, consolidation, and performance. Fibre Channel SANs provide significant advantages over direct-attached storage through improved storage utilization, higher data availability, reduced management costs, and highly scalable capacity and performance.

2. WHAT ENVIRONMENT IS MOST SUITABLE FOR FIBRE CHANNEL SANS?

          Typically, Fibre Channel SANs are most suitable for large data centers running business-critical data, as well as applications that require high-bandwidth performance such as medical imaging, streaming media, and large databases. Fibre Channel SAN solutions can easily scale to meet the most demanding performance and availability requirements.

3. WHAT CUSTOMER PROBLEMS DO FIBRE CHANNEL SANS SOLVE?

           The increased performance of Fibre Channel enables a highly effective backup and recovery approach, including LAN-free and server-free backup models. The result is a faster, more scalable, and more reliable backup and recovery solution. By providing flexible connectivity options and resource sharing, Fibre Channel SANs also greatly reduce the number of physical devices and disparate systems that must be purchased and managed, which can dramatically lower capital expenditures. Heterogeneous SAN management provides a single point of control for all devices on the SAN, lowering costs and freeing personnel to do other tasks.

4. HOW LONG HAS FIBRE CHANNEL BEEN AROUND?

           Development started in 1988, ANSI standard approval occurred in 1994, and large deployments began in 1998. Fibre Channel is a mature, safe, and widely deployed solution for high-speed (1 GB, 2 GB, 4 GB) communications and is the foundation for the majority of SAN installations throughout the world.

5. WHAT IS THE FUTURE OF FIBRE CHANNEL SANS?

        Fibre Channel is a well-established, widely deployed technology with a proven track record and a very large installed base, particularly in high-performance, business-critical data center environments. Fibre Channel SANs continue to grow and will be enhanced for a long time to come. The reduced costs of Fibre Channel components, the availability of SAN kits, and the next generation of Fibre Channel (4 GB) are helping to fuel that growth. In addition, the Fibre Channel roadmap includes plans to double performance every three years

6. WHAT ARE THE BENEFITS OF 4GB FIBRE CHANNEL?

         Benefits include twice the performance with little or no price increase, investment protection with backward compatibility to 2 GB, higher reliability due to fewer SAN components (switch and HBA ports) required, and the ability to replicate, back up, and restore data more quickly. 4 GB Fibre Channel systems are ideally suited for applications that need to quickly transfer large amounts of data such as remote replication across a SAN, streaming video on demand, modeling and rendering, and large databases. 4 GB technology is shipping today.

7. HOW IS FIBRE CHANNEL DIFFERENT FROM ISCSI?

          Fibre Channel and iSCSI each have a distinct place in the IT infrastructure as SAN alternatives to DAS. Fibre Channel generally provides high performance and high availability for business-critical applications, usually in the corporate data center. In contrast, iSCSI is generally used to provide SANs for business applications in smaller regional or departmental data centers.

8. WHEN SHOULD I DEPLOY FIBRE CHANNEL INSTEAD OF ISCSI?

          For environments consisting of high-end servers that require high bandwidth or data center environments with business-critical data, Fibre Channel is a better fit than iSCSI. For environments consisting of many midrange or low-end servers, an IP SAN solution often delivers the most appropriate price/performance.

9. Name some of the SAN topologies

Point-to-point, arbitrated loop, and switched fabric topologies

10. What's the need for separate network for storage why LAN cannot be used?

        LAN hardware and operating systems are geared to user traffic, and LANs are tuned for a fast user response to messaging requests.
With a SAN, the storage units can be secured separately from the servers and totally apart from the user network enhancing storage access in data blocks (bulk data transfers), advantageous for server-less backups.

11. What are the advantages of RAID?

  "Redundant Array of Inexpensive Disks"
Depending on how we configure the array, we can have the
- data mirrored [RAID 1] (duplicate copies on separate drives)
- striped [RAID 0] (interleaved across several drives), or
- parity protected [RAID 5](extra data written to identify errors).
These can be used in combination to deliver the balance of performance and reliability that the user requires.

12. Define RAID? Which one you feel is good choice?

RAID (Redundant array of Independent Disks) is a technology to achieve redundancy with faster I/O. There are Many Levels of RAID to meet different needs of the customer which are: R0, R1, R3, R4, R5, R10, R6.
      Generally customer chooses R5 to achieve better redundancy and speed and it is cost effective.

R0 – Striped set without parity/[Non-Redundant Array]. 

Provides improved performance and additional storage but no fault tolerance. Any disk failure destroys the array, which becomes more likely with more disks in the array. A single disk failure destroys the entire array because when data is written to a RAID 0 drive, the data is broken into fragments. The number of fragments is dictated by the number of disks in the drive. The fragments are written to their respective disks simultaneously on the same sector. This allows smaller sections of the entire chunk of data to be read off the drive in parallel, giving this type of arrangement huge bandwidth. RAID 0 does not implement error checking so any error is unrecoverable. More disks in the array means higher bandwidth, but greater risk of data loss

R1 - Mirrored set without parity.

Provides fault tolerance from disk errors and failure of all but one of the drives. Increased read performance occurs when using a multi-threaded operating system that supports split seeks, very small performance reduction when writing. Array continues to operate so long as at least one drive is functioning. Using RAID 1 with a separate controller for each disk is sometimes called duplexing.

R3 - Striped set with dedicated parity/Bit interleaved parity.

This mechanism provides an improved performance and fault tolerance similar to RAID 5, but with a dedicated parity disk rather than rotated parity stripes. The single parity disk is a bottle-neck for writing since every write requires updating the parity data. One minor benefit is the dedicated parity disk allows the parity drive to fail and operation will continue without parity or performance penalty.

R4 - Block level parity.

Identical to RAID 3, but does block-level striping instead of byte-level striping. In this setup, files can be distributed between multiple disks. Each disk operates independently which allows I/O requests to be performed in parallel, though data transfer speeds can suffer due to the type of parity. The error detection is achieved through dedicated parity and is stored in a separate, single disk unit.

R5 - Striped set with distributed parity.

Distributed parity requires all drives but one to be present to operate; drive failure requires replacement, but the array is not destroyed by a single drive failure. Upon drive failure, any subsequent reads can be calculated from the distributed parity such that the drive failure is masked from the end user. The array will have data loss in the event of a second drive failure and is vulnerable until the data that was on the failed drive is rebuilt onto a replacement drive.

R6 - Striped set with dual distributed Parity.

Provides fault tolerance from two drive failures; array continues to operate with up to two failed drives. This makes larger RAID groups more practical, especially for high availability systems. This becomes increasingly important because large-capacity drives lengthen the time needed to recover from the failure of a single drive. Single parity RAID levels are vulnerable to data loss until the failed drive is rebuilt: the larger the drive, the longer the rebuild will take. Dual parity gives time to rebuild the array without the data being at risk if one drive, but no more, fails before the rebuild is complete. 

13. What is the difference between RAID 0+1 and RAID 1+0

     RAID 0+1 (Mirrored Stripped)

In this RAID level all the data is saved on stripped volumes which are in turn mirrored, so any disk failure saves the data loss but it makes whole stripe unavailable. The key difference from RAID 1+0 is that RAID 0+1 creates a second striped set to mirror a primary striped set. The array continues to operate with one or more drives failed in the same mirror set, but if drives fail on both sides of the mirror the data on the RAID system is lost. In this RAID level if one disk is failed full mirror is marked as inactive and data is saved only one stripped volume.

   
    RAID 1+0 (Stripped Mirrored)

In this RAID level all the data is saved on mirrored volumes which are in turn stripped, so any disk failure saves data loss. The key difference from RAID 0+1 is that RAID 1+0 creates a striped set from a series of mirrored drives. In a failed disk situation RAID 1+0 performs better because all the remaining disks continue to be used. The array can sustain multiple drive losses so long as no mirror loses both its drives.

This RAID level is most preferred for high performance and high data protection because rebuilding of RAID 1+0 is less time consuming in comparison to RAID 0+1. 

14. When JBOD's are used?

    "Just a Bunch of Disks"
It is a collection of disks that share a common connection to the server, but don't include the mirroring,
striping, or parity facilities that RAID systems do, but these capabilities are available with host-based software.

15. Differentiate RAID & JBOD?

RAID: "Redundant Array of Inexpensive Disks"
Fault-tolerant grouping of disks that server sees as a single disk volume
Combination of parity-checking, mirroring, striping
Self-contained, manageable unit of storage

JBOD: "Just a Bunch of Disks"
Drives independently attached to the I/O channel
Scalable, but requires server to manage multiple volumes
Do not provide protection in case of drive failure

16. What is a HBA?

Host bus adapters (HBAs) are needed to connect the server (host) to the storage.

17. What are the advantages of SAN?

Massively extended scalability
Greatly enhanced device connectivity
Storage consolidation
LAN-free backup
Server-less (active-fabric) backup
Server clustering
Heterogeneous data sharing
Disaster recovery - Remote mirroring
While answering people do NOT portray clearly what they mean & what advantages each of them have, which are cost effective & which are to be used for the client's requirements.

18. What is the difference b/w SAN and NAS?

The basic difference between SAN and NAS, SAN is Fabric based and NAS is Ethernet based.
SAN - Storage Area Network

It accesses data on block level and produces space to host in form of disk.

NAS - Network attached Storage

It accesses data on file level and produces space to host in form of shared network folder.

19. What is a typical storage area network consists of - if we consider it for implementation in a small business setup?

          If we consider any small business following are essentials components of SAN
- Fabric Switch
- FC Controllers
- JBOD's

20. Can you briefly explain each of these Storage area components?

Fabric Switch: It's a device which interconnects multiple network devices .There are switches starting from 16 port to 32 ports which connect 16 or 32 machine nodes etc. vendors who manufacture these kind of switches are Brocade, McData.

21. FC Controllers: These are Data transfer media they will sit on PCI slots of Server; you can configure Arrays and volumes on it.

JBOD: Just Bunch of Disks is Storage Box, it consists of Enclosure where set of hard-drives are hosted in many combinations such SCSI drives, SAS, FC, SATA.

22. What is the most critical component in SAN?

Each component has its own criticality with respect to business needs of a company.

23. How is a SAN managed?

There are many management software's used for managing SAN's to name a few
- Santricity
- IBM Tivoli Storage Manager.
- CA Unicenter.
- Veritas Volumemanger.

24. Which one is the Default ID for SCSI HBA?

Generally the default ID for SCSI HBA is 7.
SCSI- Small Computer System Interface
HBA - Host Bus Adaptor

25. What is the highest and lowest priority of SCSI?

There are 16 different ID's which can be assigned to SCSI device 7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, 8.

Highest priority of SCSI is ID 7 and lowest ID is 8.

26. How do you install device drivers for the HBA first time during OS installation?

In some scenarios you are supposed to install Operating System on the drives connected thru SCSI HBA or SCSI RAID Controllers, but most of the OS will not be updated with drivers for those controllers, that time you need to supply drivers externally, if you are installing windows, you need to press F6 during the installation of OS and provide the driver disk or CD which came along with HBA.
If you are installing Linux you need to type "linux dd" for installing any driver.

27. What is Array?

Array is a group of Independent physical disks to configure any Volumes or RAID volumes.

28. Can u describe at-least 3 troubleshooting scenarios which you have come across in detail ?

SCENARIO 1: How do you find/debug when there is error while working SCSI devices?

In our daily SAN troubleshooting there are many management and configuration tools we use them to see when there is a failure with target device or initiator device.
Some time it is even hard to troubleshoot some of the things such as media errors in the drives, or some of the drives taking long time to spin-up. In such cases these utilities will not come to help. To debug this kind of information most of the controller will be implemented with 3-pin serial debug port. With serial port debug connector cable you can collect the debug information with hyper terminal software.

SCENARIO 2: I am having an issue with a controller its taking lot of time to boot and detect all the drives connected how can I solve this.?

There are many possibilities that might cause this problem. One of the reason might be you are using bad drives that cannot be repaired. In those cases you replace the disks with working ones.

Another reason might be slots you connected your controller to a slot which might not be supported.
Try to connect with other types of slots.

One more probable reason is if you have flashed the firmware for different OEM's on the same hardware.
To get rid of this the flash utilities will be having option to erase all the previous and EEPROM and boot block entry option. Use that option to rectify the problem.

SCENARIO 3: I am using tape drive series 700X, even the vendor information on the Tape drive says 700X, but the POST information while booting the server is showing as 500X what could be the problem?

First you should make sure your hardware is of which series, you can find out this in the product website.
Generally you can see this because in most of the testing companies they use same hardware to test different series of same hardware type. What they do is they flash the different series firmware. You can always flash back to exact hardware type.

29. Which are the SAN topologies?

SAN can be connected in 3 types which are mentioned below:
Point to Point topology
FC Arbitrated Loop ( FC :Fibre Channel )
Switched Fabric

30. Which are the 4 types of SAN architecture types

a. Core-edge

b. Full-Mesh

c. Partial-Mesh

d. Cascade

31. Which command is used in linux to know the driver version of any hardware device?

dmesg

32. How many minimum drives are required to create R5 (RAID 5) ?

You need to have at least 3 disk drives to create R5.

33. Can you name some of the states of RAID array?

There are states of RAID arrays that represent the status of the RAID arrays which are given below

a. Online
b. Degraded
c. Rebuilding
d. Failed

34. Name the features of SCSI-3 standard?

QAS: Quick arbitration and selection
Domain Validation

CRC: Cyclic redundancy check

35. Can we assign a hot spare to R0 (RAID 0) array?

No, since R0 is not redundant array, failure of any disks results in failure of the entire array so we cannot rebuild the hot spare for the R0 array.

36. Can you name some of the available tape media types?

There are many types of tape media available to back up the data some of them are
DLT: digital linear tape - technology for tape backup/archive of networks and servers; DLT technology addresses midrange to high-end tape backup requirements.
LTO: linear tape open; a new standard tape format developed by HP, IBM, and Seagate.
AIT: advanced intelligent tape; a helical scan technology developed by Sony for tape backup/archive of networks and servers, specifically addressing midrange to high-end backup requirements.

37. What is HA?

HA High Availability is a technology to achieve failover with very less latency. Its a practical requirement of data centers these days when customers expect the servers to be running 24 hours on all 7 days around the whole 365 days a year - usually referred as 24x7x365. So to achieve this, a redundant infrastructure is created to make sure if one database server or if one app server fails there is a replica Database or Appserver ready to take-over the operations. End customer never experiences any outage when there is a HA network infrastructure.

38. What is virtualization?

Virtualization is logical representation of physical devices. It is the technique of managing and presenting storage devices and resources functionally, regardless of their physical layout or location. Virtualization is the pooling of physical storage from multiple network storage devices into what appears to be a single storage device that is managed from a central console. Storage virtualization is commonly used in a storage area network (SAN). The management of storage devices can be tedious and time-consuming. Storage virtualization helps the storage administrator perform the tasks of backup, archiving, and recovery more easily, and in less time, by disguising the actual complexity of the SAN.

39. Describe in brief the composition of FC Frame?

Start of the Frame locator
Frame header (includes destination id and source id, 24 bytes/6 words)
Data Payload (encapsulate SCSI instruction can be 0-2112 bytes in length)
CRC (error checking, 4 bytes)
End of Frame (1 byte)

40. What is storage virtualization?

Storage virtualization is amalgamation of multiple n/w storage devices into single storage unit.

41. What are the protocols used in physical/datalink and network layer of SAN?

a) Ethernet

b) SCSI
c) Fibre Channel

42. What are the types of disk array used in SAN? 

a) JBOD
b) RAID

43. What are different types of protocols used in transportation and session layers of SAN?

a) Fibre Channel Protocol (FCP)
b) Internet SCSI (iSCSI)
c) Fibre Channel IP (FCIP)

44. What is the type of Encoding used in Fibre Channel?

8b/10b, as the encoding technique is able to detect all most all the bit errors

45. How many classes of service are available in Fibre Channel?

7 Classes of service are available in Fibre Channel

Class-1: 

         Dedicated connection between two communicators with acknowledgement of frame delivery.

       In class 1 service, a dedicated connection source and destination is established through the fabric for the duration of the transmission. It provides acknowledged service. This class of service ensures that the frames are received by the destination device in the same order in which they are sent, and reserves full bandwidth for the connection between the two devices. It does not provide for a good utilization of the available bandwidth, since it is blocking another possible contender for the same device. Because of this blocking and necessary dedicated connection, class 1 is rarely used.

Class-2: 

          connection less but provides acknowledgement

Class 2 is a connectionless, acknowledged service. Class 2 makes better use of available bandwidth since it allows the fabric to multiplex several messages on a frame-by-frame basis. As frames travel through the fabric they can take different routes, so class 2 service does not guarantee in-order delivery. Class 2 relies on upper layer protocols to take care of frame sequence. The use of acknowledgments reduces available bandwidth, which needs to be considered in large-scale busy networks.

Class-3: 

               connection less and provides no notification of delivery
There is no dedicated connection in class 3 and the received frames are not acknowledged. Class 3 is also called datagram connectionless service. It optimizes the use of fabric resources, but it is now upper layer protocol to ensure that all frames are received in the proper order, and to request to the source device the retransmission of missing frames. Class 3 is a commonly used class of service in Fibre Channel networks.

Class-4: 
               
                 allows fractional bandwidth for virtual circuits

      Class 4 is a connection-oriented service like class 1, but the main difference is that it allocates only a fraction of available bandwidth of path through the fabric that connects two N_Ports. Virtual Circuits (VCs) are established between two N_Ports with guaranteed Quality of Service (QoS), including bandwidth and latency. Like class 1, class 4 guarantees in-order delivery frame delivery and provides acknowledgment of delivered frames, but now the fabric is responsible for multiplexing frames of different VCs. Class 4 service is mainly intended for multimedia applications such as video and for applications that allocate an established bandwidth by department within the enterprise. Class 4 was added in the FC-PH-2 standard.

Class -5: 

       Class 5 is called isochronous service, and it is intended for applications that require immediate delivery of the data as it arrives, with no buffering. It is not clearly defined yet. It is not included in the FC-PH documents.

Class-6: 

      Provides multicast, dedicated connection with acknowledgment
Class 6 is a variant of class 1, known as multicast class of service. It provides dedicated connections for a reliable multicast. An N_Port may request a class 6 connection for one or more destinations. A multicast server in the fabric will establish the connections and get acknowledgment from the destination ports, and send it back to the originator. Once a connection is established, it should be retained and guaranteed by the fabric until the initiator ends the connection. Class 6 was designed for applications like audio and video requiring multicast functionality. It appears in the FC-PH-3 standard.

Class-F: 

       used for switch to switch communication in the fabric.
Class F service is defined in the FC-SW and FC-SW-2 standard for use by switches communicating through ISLs. It is a connectionless service with notification of non-delivery between E_Ports used for control, coordination, and configuration of the fabric. Class F is similar to class 2; the main difference is that Class 2 deals with N_Ports sending data frames, while Class F is used by E_ports for control and management of the fabric.