What are the performance issues with RAID 6 or dual-parity schemes?

With RAID 6, you can theoretically get double the data protection without doubling the number of drives. But you'll need to work around the performance penalty.

It sounds great: Go to RAID 6 and get double the protection without doubling the number of drives.

However, as with RAID 5, there is a performance penalty on writes that is typically offset by cache, faster processors or hardware assists. Now you are doing two RAID calculations and two parity updates. That means you're doing twice the calculations and twice the work, so you need to have the performance to counter that.

RAID information
RAID levels defined

Do RAID levels still matter?

How to calculate available disk space on a RAID 5

There are several ways to accomplish this. Some systems leverage hardware offloads to perform the extra calculations to assist with data movement. Some systems simply rely on software. Other systems use a combination of software and a hardware offload ASIC or assist. Some systems are optimized for large writes, others for small. Some are optimized for reads and writes. in any case, you need to understand how RAID 6 is implemented, how it is deployed and what tradeoffs come with it.

Check out the entire RAID FAQ guide.

 

This was first published in November 2007

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