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SUN StorageTek’s RAID 6 Implementation


Continuing the series on RAID 6 technology with different OEM products; this time around it’s SUN StorageTek version of RAID 6 implementation on 6xxx series arrays.

Here are the links to previous posts related to RAID 6. It covers NetApp’s RAID-DP, Hitachi’s RAID 6, HP’s RAID 6 and technical post on various different RAID technologies.

HP’s RAID 6

NetApp’s RAID–DP

Hitachi’s (HDS) RAID 6

Different RAID Technologies (Detailed)

Different RAID Types

SUN’s Business Case

Similar to HP, Sun is not making a claim on performance with RAID 6; its only claim with this technology implementation on its products is Improved Reliability.

RAID 6 is supported on SUN StorageTek’s 6140, 6580 and 6780 Arrays

SUN StorageTek products traditionally support RAID 0, RAID 1, RAID 3, RAID 5, RAID 1+0 and now RAID 6.

Different Applications that can use RAID 6 technology on SUN StorageTek arrays are Exchange Email, Web Servers, File Servers, Oracle, SAP, SQL and MySQL.

Technology

Here is a small abstract about RAID 6 Technology as discussed in my earlier post.

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

Performance: Medium

Overhead: 10% to 50% overhead, with additional drives you can bring down the overhead.

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

Advantages: RAID 6 is essentially an extension of RAID 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: Poor Write performance in addition to requiring N+2 drives to implement because of P+Q parity scheme.

The technology (P+Q Parity Algorithm) of Sun’s implementation and HP’s implementation of RAID 6 is similar. To further read about HP’s RAID 6, please use the link below.

HP’s RAID 6

The formula to calculate your usable space with RAID 6 is C * (n – 2), where C is the Size of your smallest drive in the RAID Group and n = number of drives. It is highly recommended all your disk drive sizes are similar.

The largest configuration of RAID 6 can be 257 drives with 2 parity drives and 255 data drives. Usage of more drives will help bring down the RAID 6 overhead since 2 drives are always allocated as parity.

This technology can be implemented with a minimum of 4 drives. The overhead with use of 4 drives in a single RAID Group is 50%. If you run 60 drives in a single RAID group, your overhead might be close to 4% {100 – [100 x 2 (parity) / 60 (drives)]}.

Lower write performance is a unique disadvantage of using RAID 6.

Both Sun StorageTek’s RAID 6 and HP’s RAID 6 offers advantages related to reliability and data protection but no additional benefits with performance, capacity, efficiency, speed, etc.

We will leave it up to the user to decide what RAID technology best fits their environment on SUN StorageTek 6XXX arrays for various different applications.