RAIDZ with 4 drives okay?

[Pie]

Hi,

I've spent the better part of an hour reading through posts about RAIDZ and it seems like everyone recommends 5 drives for RAIDZ and 4 drives for RAIDZ2. Is it okay to use 4 drives for RAIDZ? Are there penalties to consider?

Thanks!

 

[jgreco]

Yes, there are penalties to consider. But it'll work.

Check out the ZFS Best Practices Guide if you want to find out more. I also recently posted a table that lists the full set of possibilities for optimally-sized RAIDZ's, see this thread.

It is possible to go with vdevs that are wider than a dozen disks or other numbers of disks besides the power-of-two-plus-parity selections, but you start to get into penalties of various sorts.

 

[HAL 9000]

Check out the ZFS Best Practices Guide if you want to find out more

"Start a single-parity RAIDZ (raidz) configuration at 3 disks (2+1)"
so 4 drives should be perfect.

numbers of disks besides the power-of-two-plus-parity selections, but you start to get into penalties of various sorts.

What penalties and why? Could you explain pls?

 

[ben]

http://mail.opensolaris.org/pipermail/zfs-discuss/2010-September/044701.html I found this email, referring to a thread on a defunct forum. From what I can tell, it's a rounding issue with non-power-of-two data disks in a RAID-Z* group. This seems to suggest it's primarily space saving. It's not critical to go with powers of two plus parity, but it is recommended just about everywhere you look.