RAID5 vs. RAID6

You might want to review the two docuements - the first is an overview of Raid 6, the second is a Best Practices guide - it has section about using the different Raid Types and when to use R5 or R6.

White Paper: EMC CLARiiON RAID 6 Technology - A Detailed Review

http://powerlink.emc.com/km/live1/en_US/Offering_Technical/White_Paper/H2891-clariion-raid-6.pdf

EMC CLARiiON Performance and Availability Release 28.5 Firmware Update Applied Best Practices.pdf

http://powerlink.emc.com/km/live1/en_US/Offering_Technical/White_Paper/h5773-clariion-perf-availability-release-28-firmware-wp.pdf

glen

Consider this:
RAID6 gives you double the redundancy over ALL drives, so if drives 1 and 2 fail, you're still safe. If this would happen in 2 x (4+1) Raid 5, your first RG will be dead and your LUN is dead as well. But you pay the price, since R6 has to write 2 times the parity for ALL writes, where 2 x R5 only writes the parity once (in the RG where the I/O actually took place) and 2 x R5 is therefore faster. But 2 x R5 is not as safe !

Raid5 = faster
Raid6 = safer

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RRR
added 2 extra lines

You would have to fully understand your workload and your availability requirement to determine which grouping is best for you.

As previously mentioned, the capacity of the two RAID group organizations would be the same in terms of raw storage. The built-in availability of the two groupings is different. Likewise, the performance would be different under certain conditions.

Generally, the RAID 6 organization for 10 disks is going to have greater availability.

In fully cached ¿normal¿ operation with recommended LUN utilizations, you will observe no difference in the performance of the two organizations. Uncached performance and degraded-mode performance are different. Note there are many ways you can end-up in uncached operation.

Uncached, the MetaLUN organization will likely have better performance. How large a performance advantage it will have depends on the workload. The size of this advantage depends on the ratio of writes to reads, and how writes and reads are performed (random or sequential).

The big factor in the performance difference between the MetaLUN and RAID 6 group is write performance. The higher the proportion of writes to reads in the workload, the bigger the MetaLUNs performance advantage. Random read performance of the two organizations will be slightly better for the MetaLUN. The MetaLUN is better at random writes.

Generally, the more sequential the nature of the workload, the smaller the observable MetaLUN performance advantage. There is no performance difference between the two with a 100% sequential read workload. The MetaLUN is better performing with sequential writes.

Finally, either RAID 5 group will rebuild faster than the larger RAID 6 group in the event of a single disk failure. That is, the MetaLUN organization will spend a shorter time in degraded mode than the RAID 6 organization.

Making the correct choice requires you to understand your workload and availability commitment. The EMC CLARiiON Storage System Fundamentals for Performance and Availability document available on Powerlink discusses how to make a decision in the ¿Workload¿ section.

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jps00

I'd recommend the Clariion Performance Workshop. I had an excellent instructor back then and I can promise you, you'll learn a whole lot more then by just trial and error and reading manuals