RAIDZ2 with 7 Disks?

[haziz]

Most discussions of RAIDZ2 refer to 6 or 10 disks as ideal. Is there a significant (or for that matter any) penalty to using 7 drives (7 x 3TB) in a RAIDZ2 configuration?

Thanks.

 

[William Grzybowski]

Sure, writes/reads wont be aligned but you probably wont notice unless you're on 10GbE...

 

[haziz]

Sure, writes/reads wont be aligned but you probably wont notice unless you're on 10GbE...

Can you elaborate on what you mean by "writes/reads wont be aligned"? A link to a FAQ or Wiki would also be OK. I am fairly savvy with Unix but not with ZFS and this is my first time setting up a NAS.

Thanks.

 

[William Grzybowski]

Well, it is a basic understanding of how raid works... block sizes are on base of 2, blocks are spread between disks + parity, if the number disks is not power of two the pieces of the block will not be equally distributed between disks, resulting in "unaligned" read/writes, one or more disks will have more or less data for a given piece...

I don't have any docs to point you...

 

[jgreco]

There's a penalty and it can come into play long before 10GbE, but it is not an absolutely compelling concern.

http://mail.opensolaris.org/pipermail/zfs-discuss/2010-September/044701.html

 

[Stephens]

OP FYI... with reads/writes over the network it may not be noticeable, but it also affects local traffic like scrubs and resilvers (drive replacement), or initial loading of a pool via copying from mounted drive(s) external to the pool. As the guys have said, it may not be a concern as long as you're aware of it.