ZFS RAIDZ stripe width, or: How I Learned to Stop Worrying and Love RAIDZ

[Philip Robar]

I posted a reference to this short article on Google+ and it's been quite popular so I figure that folks here would also find it to be useful.

Matthew Ahrens is one of original designers of ZFS and is still active in its development.

Matthew Ahrens: ZFS RAIDZ stripe width, or: How I Learned to Stop Worrying and Love RAIDZ​

The popularity of OpenZFS has spawned a great community of users, sysadmins, architects and developers, contributing a wealth of advice, tips and tricks, and rules of thumb on how to configure ZFS. In general, this is a great aspect of the ZFS community, but I’d like to take the opportunity to address one piece of misinformed advice about how many disks to put in each RAID-Z group (terminology: “zpool create tank raidz1 A1 A2 A3 A4 raidz1 B1 B2 B3 B4” has 2 RAIDZ groups or “vdevs”, each of which has 4 disks or is “4-wide”). To do so, let’s start by looking at what concerns play into choice of group width.

TL;DR: Choose a RAID-Z stripe width based on your IOPS needs and the amount of space you are willing to devote to parity information. If you need more IOPS, use fewer disks per stripe. If you need more usable space, use more disks per stripe. Trying to optimize your RAID-Z stripe width based on exact numbers is irrelevant in nearly all cases.​

 

[cyberjock]

Thanks for providing the document. It is appreciated. But most of us have seen it already. That document is part of the reason why the manual says you don't have to try to optimize your RAIDZ layout. It's also why my FreeNAS Noobie presentation says that you can ignore the RAIDZ layouts with regards to optimization if you plan to use compression. :P