RAID Technology in DMX / Symmetrix Continued

RAID [Redundant Array of Independent (Inexpensive) Disk]

After reading couple of Blogs from last week regarding RAID Technology from StorageSearch and StorageIO, decided to elaborate more about the technology behind RAID and its functionality across Storage Platforms.

After I almost finished writing this blog, I ran into a Wikipedia article explaining RAID TECHNOLOGY at a much length, covering different types of RAID technologies like RAID 2, RAID 4, RAID 10, RAID 50, etc.

For example purposes, let’s say we need 5 TB of Space; each disk in this example is 1 TB each.

RAID 0

Technology: Striping Data with No Data Protection.

Performance: Highest

Overhead: None

Minimum Number of Drives: 2 since striping

Data Loss: Upon one drive failure

Example: 5TB of usable space can be achieved through 5 x 1TB of disk.

Advantages:
> High Performance

Disadvantages: Guaranteed Data loss

Hot Spare: Upon a drive failure, a hot spare can be invoked, but there will be no data to copy over. Hot Spare is not a good option for this RAID type.

Supported: Clariion, Symmetrix, Symmetrix DMX (Meta BCV’s or DRV’s)

In RAID 0, the data is written / stripped across all of the disks. This is great for performance, but if one disk fails, the data will be lost because since there is no protection of that data.

RAID 1

Technology: Mirroring and Duplexing

Performance: Highest

Overhead: 50%

Minimum Number of Drives: 2

Data Loss: 1 Drive failure will cause no data loss. 2 drive failures, all the data is lost.

Example: 5TB of usable space can be achieved through 10 x 1TB of disk.

Advantages: Highest Performance, One of the safest.

Disadvantages: High Overhead, Additional overhead on the storage subsystem. Upon a drive failure it becomes RAID 0.
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Hot Spare: A Hot Spare can be invoked and data can be copied over from the surviving paired drive using Disk copy.

Supported: Clariion, Symmetrix, Symmetrix DMX

The exact data is written to two disks at the same time. Upon a single drive failure, no data is lost, no degradation, performance or data integrity issues. One of the safest forms of RAID, but with high overhead. In the old days, all the Symmetrix supported RAID 1 and RAID S. Highly recommended for high end business critical applications.

The controller must be able to perform two concurrent separate Reads per mirrored pair or two duplicate Writes per mirrored pair. One Write or two Reads are possible per mirrored pair. Upon a drive failure only the failed disk needs to be replaced.

RAID 1+0

Technology: Mirroring and Striping Data

Performance: High

Overhead: 50%

Minimum Number of Drives: 4

Data Loss: Upon 1 drive failure (M1) device, no issues. With multiple drive failures in the stripe (M1) device, no issues. With failure of both the M1 and M2 data loss is certain.

Example: 5TB of usable space can be achieved through 10 x 1TB of disk.

Advantages: Similar Fault Tolerance to RAID 5, Because of striping high I/O is achievable.

Disadvantages: Upon a drive failure, it becomes RAID 0.

Hot Spare: Hot Spare is a good option with this RAID type, since with a failure the data can be copied over from the surviving paired device.

Supported: Clariion, Symmetrix, Symmetrix DMX

RAID 1+0 is implemented as a mirrored array whose segments are RAID 0 arrays.

RAID 3

Technology: Striping Data with dedicated Parity Drive.

Performance: High

Overhead: 33% Overhead with Parity (in the example above), more drives in Raid 3 configuration will bring overhead down.

Minimum Number of Drives: 3

Data Loss: Upon 1 drive failure, Parity will be used to rebuild data. Two drive failures in the same Raid group will cause data loss.

Example: 5TB of usable space would be achieved through 9 1TB disk.

Advantages: Very high Read data transfer rate. Very high Write data transfer rate. Disk failure has an insignificant impact on throughput. Low ratio of ECC (Parity) disks to data disks which converts to high efficiency.

Disadvantages: Transaction rate will be equal to the single Spindle speed

Hot Spare: A Hot Spare can be configured and invoked upon a drive failure which can be built from parity device. Upon drive replacement, hot spare can be used to rebuild the replaced drive.

Supported: Clariion

RAID 5

Technology: Striping Data with Distributed Parity, Block Interleaved Distributed Parity

Performance: Medium

Overhead: 20% in our example, with additional drives in the Raid group you can substantially bring down the overhead.

Minimum Number of Drives: 3

Data Loss: With one drive failure, no data loss, with multiple drive failures in the Raid group data loss will occur.

Example: For 5TB of usable space, we might need 6 x 1 TB drives

Advantages: It has the highest Read data transaction rate and with a medium write data transaction rate. A low ratio of ECC (Parity) disks to data disks which converts to high efficiency along with a good aggregate transfer rate.

Disadvantages: Disk failure has medium impact on throughput. It also has most complex controller design. Often difficult to rebuild in the event of a disk failure (as compared to RAID level 1) and individual block data transfer rate same as single disk. Ask the PSE’s about RAID 5 issues and data loss?

Hot Spare: Similar to RAID 3, where a Hot Spare can be configured and invoked upon a drive failure which can be built from parity device. Upon drive replacement, hot spare can be used to rebuild the replaced drive.

Supported: Clariion, Symmetrix DMX code 71

RAID Level 5 also relies on parity information to provide redundancy and fault tolerance using independent data disks with distributed parity blocks. Each entire data block is written onto a data disk; parity for blocks in the same rank is generated on Writes, recorded in a distributed location and checked on Reads.

This would classify to be the most favorite RAID Technology used today.

RAID 6

Technology: Striping Data with Double Parity, Independent Data Disk with Double Parity

Performance: Medium

Overhead: 28% in our example, with additional drives you can bring down the overhead.

Minimum Number of Drives: 4

Data Loss: With one drive failure and two drive failures in the same Raid Group no data loss. Very reliable.

Example: For 5 TB of usable space, we might need 7 x 1TB drives

Advantages: RAID 6 is essentially an extension of RAID level 5 which allows for additional fault tolerance by using a second independent distributed parity scheme (two-dimensional parity). Data is striped on a block level across a set of drives, just like in RAID 5, and a second set of parity is calculated and written across all the drives; RAID 6 provides for an extremely high data fault tolerance and can sustain multiple simultaneous drive failures which typically makes it a perfect solution for mission critical applications.

Disadvantages: Very poor Write performance in addition to requiring N+2 drives to implement because of two-dimensional parity scheme.

Hot Spare: Hot Spare can be invoked against a drive failure, built it from parity or data drives and then upon drive replacement use that hot spare to build the replaced drive.

Supported: Clariion Flare 26, 28, Symmetrix DMX Code 72, 73

Clariion Flare Code 26 supports RAID 6. It is also being implemented with the 72 code on the Symmetrix DMX. The simplest explanation of RAID 6 is double the parity. This allows a RAID 6 RAID Groups to be able to have two drive failures in the RAID Group, while maintaining access to the data.

RAID S (3+1)

Technology: RAID Symmetrix

Performance:
> High

Overhead: 25%

Minimum Number of Drives: 4

Data Loss: Upon two drive failures in the same Raid Group

Example: For 5 TB of usable space, 8 x 1 TB drives

Advantages: High Performance on Symmetrix Environment

Disadvantages: Proprietary to EMC. RAID S can be implemented on Symmetrix 8000, 5000 and 3000 Series. Known to have backend issues with director replacements, SCSI Chip replacements and backend DA replacements causing DU or offline procedures.

Hot Spare: Hot Spare can be invoked against a failed drive, data can be built from the parity or the data drives and upon a successful drive replacement, the hot spare can be used to rebuild the replaced drive.

Supported: Symmetrix 8000, 5000, 3000. With the DMX platform it is just called RAID (3+1)

EMC Symmetrix / DMX disk arrays use an alternate, proprietary method for parity RAID that they call RAID-S. Three Data Drives (X) along with One Parity device. RAID-S is proprietary to EMC but seems to be similar to RAID-5 with some performance enhancements as well as the enhancements that come from having a high-speed disk cache on the disk array.

The data protection feature is based on a Parity RAID (3+1) volume configuration (three data volumes to one parity volume).

RAID (7+1)

Technology: RAID Symmetrix

Performance: High

Overhead: 12.5%

Minimum Number of Drives: 8

Data Loss: Upon two drive failures in the same Raid Group

Example: For 5 TB of usable space, 8 x 1 TB drives (rather you will get 7 TB)

Advantages: High Performance on Symmetrix Environment

Disadvantages: Proprietary to EMC. Available only on Symmetrix DMX Series. Known to have a lot of backend issues with director replacements, backend DA replacements since you have to verify the spindle locations. Cause of concern with DU.

Hot Spare: Hot Spare can be invoked against a failed drive, data can be built from the parity or the data drives and upon a successful drive replacement, the hot spare can be used to rebuild the replaced drive.

Supported: With the DMX platform it is just called RAID (7+1). Not supported on the Symms.

EMC DMX disk arrays use an alternate, proprietary method for parity RAID that is called RAID. Seven Data Drives (X) along with One Parity device. RAID is proprietary to EMC but seems to be similar to RAID-S or RAID5 with some performance enhancements as well as the enhancements that come from having a high-speed disk cache on the disk array.

The data protection feature is based on a Parity RAID (7+1) volume configuration (seven data volumes to one parity volume).

RAID Technology in DMX / Symmetrix

Various Implementations of RAID Types with EMC Symmetrix / DMX and Clariion Technology.

RAID (Redundant Array of Inexpensive or Independent Disk)

RAID 0 – Striped Disk Array without Fault Tolerance: Provides data striping (spreading out blocks of each file across multiple disk drives) but no redundancy. This improves performance but does not deliver fault tolerance. If one drive fails then all data in the array is lost.

RAID 1 – Mirroring and Duplexing: Provides disk mirroring. Level 1 provides twice the read transaction rate of single disks and the same write transaction rate as single disks.

RAID 5 – Block Interleaved Distributed Parity: Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance. Level 5 is one of the most popular implementations of RAID.

Now Available 3 RAID 5 and 7 RAID 5 with EMC DMX Platform.

RAID 6 – Independent Data Disks with Double Parity: Provides block level striping with parity data distributed across all disks.

RAID 0 + 1 – A Mirror of Stripes: Not one of the original RAID levels, two RAID 0 stripes are created, and a RAID 1 mirror is created over them. Used for both replicating and sharing data among disks.

RAID S (3 + 1): EMC Symmetrix / DMX disk arrays use an alternate, proprietary method for parity RAID that they call RAID-S. Three Data Drives (X) along with One Parity device. RAID-S is proprietary to EMC but seems to be similar to RAID-5 with some performance enhancements as well as the enhancements that come from having a high-speed disk cache on the disk array.

RAID S (7+1): EMC DMX disk arrays use an alternate, proprietary method for parity RAID that they call RAID-S. Seven Data Drives (X) along with One Parity device. RAID-S is proprietary to EMC but seems to be similar to RAID-5 with some performance enhancements as well as the enhancements that come from having a high-speed disk cache on the disk array

EMC Clariion RAID-6 requirements and limitations

Here are some requirements and limitations related to using the RAID-6 technology on the EMC Clariion platforms.

• RAID-6 is only supported with Flare Release 26 and above on Clariion systems.
• Flare 26 only works on the EMC Clariion CX300, CX500, CX700, all CX3-xx platforms and all CX4-xxx platforms.|
• Any systems running below Flare Release 26 (example Release 13, 16, 19, 24) are not compatible to run RAID-6 (Clariion Systems like CX200, CX400 and CX600).

• Minimum disk required to support RAID-6 with Clariion systems is 2 or 4 or 6 or 8 or 14 data disks with 2 Parity disks (Your typical configuration would look like 2D+2P or 4D+2P or 6D+2P or 8D+2P or 14D+2P, where D = Data Disk and P = Parity Disk)
• To configure RAID-6, you will need even number of disk drives in the RAID Group that you are trying to configure.
• RAID-6 is supported on either EFD (Enterprise Flask Disk) or Fiber (FC) or ATA or SATA drives on EMC Clariion Systems.
• RAID-6 Raid group (RAID SET) can be implemented within an enclosure or expanded beyond a single enclosure
• RAID-6 can co-exist in the same DAE (disk array enclosure) as a RAID-5 and/or RAID-1/0 and/or other RAID types.
• RAID-6 supports global hot sparing like other RAID technologies.
• Supports MetaLUN expansion through concatenated or striped expansion only if all the meta member LUNs are RAID-6 devices (LUNs).
• RAID-6 configuration is possible through Navisphere and naviseccli only.
• With RAID-6 traditionally supported CLI interfaces like Java CLI and Classic CLI have been retired.
• Defragmentation with RAID-6 is currently not supported on Flare Release 26.
• You cannot add new drives to an existing RAID-6 LUN, but you can expand the LUN through RAID-6 MetaLUN technology. Example of this will be, if you have a 6D+2P RAID-6 set and would like to add 16 more drives to the same RAID Group, you cannot accomplish it, but if you manage to create either 2 sets of 6D+2P or 1 set of 14D+2P, and then run a MetaLUN concatenate, you will be able to necessarily achieve the same end result.
• You can have Clariion systems with various different RAID group technologies in the same global domain, but again from a management perspective certain traditional CLI interfaces will not work with RAID-6.
• Using the Virtual LUN Technology with Flare Release 26, now customers can migrate various LUNs (RAID-5, RAID-1/0) to RAID-6 technology. The technology allows the new RAID-6 LUN to assume the exact identity of the previous LUN making the migration process much easy.
• Traditional replication and copy software’s like SANCopy, SnapView, MirrorView, and RecoverPoint are all supported for RAID-6 technology.
• Never use RAID-6 technology with a mix of EFD, FC, ATA and SATA drives in the same RAID Group.
• Never use RAID-6 technology with a mix of various drive speeds like 15K or 10K or 7.2K RPM, drive speed should be exactly similar.

• Oh the most important note: 2 drive failures in the same RAID Group and no data loss or data unavailable (DU / DL), making this a very robust RAID technology. There are some performance overhead related to use of RAID-6 systems with small and random writes. While there is an added penalty with Row Parity and Diagonal Parity calculations on the Clariion.

If you would like to see any further post on RAID-6 workings on Clariion Platforms, please feel free to leave a comment.

To read about other RAID-6 implementations with various platforms, please see below.

CLARIION Features

Data intigrity

-How Clariion keeps data safe ..?

•   Mirrored write cache , Vault ..etc.

Data Availability

-How Ensuring Uninterrupted host access to data..?

• Hardware redundency , Path failover software (Powerpath), Error reporting Capability.

Clariion Performance

-What makes a Clariion a great performer..?

• Cache , Dual SPs ,Dual/Quad Back-end FC Buses

Clariion Storage Objects

-A First look at LUNs, and access to them

• RAID Groups , LUNS, MetaLUNs, StorageGroups.

RAID groups , types

RAID GROUPS and RAID Types

     The above slide illustrates the concept of creating a RAID Group and the supported RAID types of the Clariions.

RAID Groups

   The concept of a RAID Group on a Clariion is to group together a number of disks on the Clariion into one big group. Let’s say that we need a 1 TB LUN. The disks we have a 200 GB in size. We would have to group together five (5) disks to get to the 1 TB size needed for the LUN. I know we haven’t taken into account for parity and what the RAW capacity of a drive is, but that is just a very basic idea of what we mean by a RAID Group. RAID Groups also allow you to configure the Clariion in a way so that you will know what LUNs, Applications, etc…live on what set of disks in the back of the Clariion. For instance, you wouldn’t want an Oracle Database LUN on the same RAID Group (Disks) as a SQL Database running on the same Clariion. This allows you to create a RAID Group of a # of disks for the Oracle Database, and another RAID Group of a different set of disks for the SQL Database.

RAID Types

Above are the supported RAID types of the Clariion.

RAID 0 – Striping Data with NO Data Protection.

    The Clariions Cache will write the data out to disk in blocks (chunks) that we will discuss later. For RAID 0, the Clariion writes/stripes the data across all of the disks in the RAID Group. This is fantastic for performance, but if one of the disks fail in the RAID 0 Group, then the data will be lost because there is no protection of that data (i.e. mirroring, parity).

RAID 1 – Mirroring. 

    The Clariion will write the Data out to the first disk in the RAID Group, and write the exact data to another disk in that RAID 1 Group. This is great in terms of data protection because if you were to lose the data disk, the mirror would have the exact copy of the data disk, allowing the user to access the disk.

RAID 1_0 – Mirroring and Striping Data. 

   This is the best of both worlds if set up properly. This type of RAID Group will allow the Clariion to stripe data and mirror the data onto other disks. However, the illustration above of RAID 1_0, is not the best way of configuring that type of RAID Group. The next slide will go into detail as to why this isn’t the best method of configuring RAID 1_0.

RAID 3 – Striping Data with a Dedicated Parity Drive. 

    This type of RAID Group allows the Clariion to stripe data the first X number of disks in the RAID Group, and dedicate the last disk in the RAID Group for Parity of the data stripe. In the event of a single drive failure in this RAID Group, the failed disk can be rebuilt from the remaining disks in the RAID Group.

RAID 5 – Striping Data with Distributed Parity.

   RAID type 5 allows the Clariion to distribute the Parity information to rebuild a failed disk across the disks that make up the RAID Group. As in RAID 3, in the event of a single drive failure in this RAID Group, the failed disk can be rebuilt from the remaining disks in the RAID Group.

RAID 6 – Striping Data with Double Parity. 

      This is new to Clariion world starting in Flare Code 26 of Navisphere. The simplest explanation of RAID 6 we can use for RAID 6 is the RAID Group uses striping, such as RAID 5, with double the parity. This allows a RAID 6 RAID Group to be able to have two drive failures in the RAID Group, while maintaining access to the LUNs.

HOT SPARE – A Dedicated Single Disk that Acts as a Failed Disk. 

     A Hot Spare is created as a single disk RAID Group, and is bound/created as a HOT SPARE in Navisphere. The purpose of this disk is to act as the failed disk in the event of a drive failure. Once a disk is set as a HOT SPARE, it is always a HOT SPARE, even after the failed disk is replaced. In the slide above, we list the steps of a HOT SPARE taking over in the event of a disk failure in the Clariion. 
1. A disk fails – a disk fails in a RAID Group somewhere in the back of the Clariion.

2. Hot Spare is Invoked – a Clariion dedicated HOT SPARE acts as the failed disk in Navisphere. It will assume the identity of the failed disk’s Bus_Enclosure_Disk Address.

3. Data is REBUILT Completely onto the Hot Spare from the other disks in the RAID Group – The Clariion begins to recalculate and rebuild the failed disk onto the Hot Spare from the other disks in the RAID Group, whether it be copying from the MIRRORed copy of the disk, or through parity and data calculations of a RAID 3 or RAID 5 Group.

4. Disk is replaced – Somewhere throughout the process, the failed drive is replaced.

5. Data is Copied back to new disk – The data is then copied back to the new disk that was replaced. This will take place automatically, and will not begin until the failed disk is completely rebuilt onto the Hot Spare.

6. Hot Spare is back to a Hot Spare – Once the data is written from the Hot Spare back to the failed disk, the Hot Spare goes back to being a Hot Spare waiting for another disk failure.

Hot Spares are going to be size and drive type specific.

Size. 

   The Hot Spare must be at least the same size as the largest size disk in the Clariion. A Hot Spare will replace a drive that is the same size or a smaller size drive. The Clariion does not allow multiple smaller Hot Spares replace a failed disk.

Drive Type Specific.

    If your Clariion has a mixture of Drive Types, such as Fibre and S.ATA disks, you will need Hot Spares of those particular Drive Types. A Fibre Hot Spare will not replace a failed S.ATA disk and vice versa.

Hot Spares are not assigned to any particular RAID Group. They are used by the Clariion in the event of any failure of that Drive Type. The recommendation for Hot Spares is one (1) Hot Spare for every thirty (30) disks.

   There are multiple ways to create a RAID Group. One is via the Navisphere GUI, and the other is through the Command Line Interface. In later slides we will list the commands to create a RAID Group.

CLARiiON LAB Exercise - Session -I

       I am going to demonstrate full LAB exercise of CLARiiON. If anybody interested to any specific LAB exercise please send me mail I will try to help and give LAB exercise. There are many exercise like:

1) Create RAID Group

2) Bind the LUN

3) Create Storage Group

4) Register the Host

5) Present LUN to Host

6) Create Meta LUN etc.

    I will try to cover all the exercise including if you need anything extra exercise. Very Easy way to allocate the storage using Allocation wizard provided everything connected and visible to CLARiiON.

CLARiiON LAB Session -I

            I am going to demonstrate LAB Exercise for Allocation Storage to Host from CX Array using Allocation Wizard of Navisphere  Manager. I will be giving demo other method as well like allocating storage without wizard because some time host will not login to CX Frame. I will be discussing command line as well who are more interested in scripting.

Steps 1:

Login to Navisphere Manager ( Take any IP of any SP's in your domain and type on browser). You can see the all the clariion listing under each Domain.

Steps 2: Click Allocation on Left Side Menu Tree.

Steps 3: Click next once you have selected Host name (Whom you are going to present LUN) You can select Assign LUN to this server or you can continue without assigning.

Steps 4: Select Next and Select CX frame where you want to create LUN.

Steps 5: Select Next, If you have created RAID Group It will be listed here otherwise you can create new Raid Group by selecting New Raid Group.( I will be discussing later how to create different RAID Group)

Steps 6: Select RAID Group ID and depending on Raid Group select number of disk for example if you are creating Raid 5 (3+1) then select 4 disks. Once You have created raid group. It will list under RAID Group dialog box.Click Next and select the Number of LUN you want to create on same RAID Group. For example RAID Group created for 3+1 disk of 500 GB each disk means you can use roughly 500X4X70%
GB. Now you want to create different size of each LUN on the same RAID Group

Steps 7: Once you have selected Number of LUN and Size of LUN. You can verify the configuration before you run the finish button.

Steps 8: Once you click the Finish Button you can see the status. System will create Storage Group with Server Name (You can change storage group name later) and add created LUN into storage Group.
You can verify the entire configuration by clicking storage group name:

    This is end of first CLARiiON LAB exercise. Hope this exercise will be useful for beginner. I will try to cover as much i can for all the EMC product lab exercise. If anybody interested to clear the any EMC Proven foundation

RAID types

 RAID configurations enables  us to expand characteristics of storage value beyond the physical limitations of single disk.

Importance of RAID is to provide redundancy and increase the performance , fault tolerance.

RAID : Redundant Array of Independent Disks 

          Main RAID types are :

               

                RAID 0 : Concatenation or Striping. (not providing fault tolerance)

                RAID 1 : Mirroring.

                RAID 2 : Hamming code

                RAID 3 : All parity is stored into one disk. (similar to raid 2)

                RAID 4 : similar to raid 3

                RAID 5 : Striping with parity. (only one time tolerance)

                RAID 6 : raid 5 with extra parity disk.

                And Combinations like RAID 0+1 , RAID 1+0 . (hybrid)

                Hybrid levels : (Combinations of original RAID groups)

               RAID level 10 : Mirroring with striping.

               RAID level 30 : Parity RAID techniques with data striping.

               RAID level 50 : Parity RAID techniques with data striping.