optimal vdev size

[Johnny Fartpants]

When building zfs storage I've always kept to the following rule.

"The following ZFS pool configurations are optimal for modern 4K sector harddrives: RAID-Z 3, 5, 9, 17, 33 drives RAID-Z2: 4, 6, 10, 18, 34 drives RAID-Z3: 5, 7, 11, 19, 35 drives"

A recent project has caused me to question this as it would make my life easier if for example I could use 9 drives in a RAID-Z2 and not 10 due to chassis size.

I would be interested to hear your thoughts on this and if you consider this a hard and fast rule or quite the opposite just ignore it and configure your vdevs to suit your needs.

 

[dlavigne]

From http://doc.freenas.org/9.3/freenas_intro.html#zfs-primer:

Some older ZFS documentation recommends that a certain number of disks is needed for each type of RAIDZ in order to achieve optimal performance. On systems using LZ4 compression, which is the default for FreeNAS® 9.2.1 and higher, this is no longer true. See ZFS RAIDZ stripe width, or: How I Learned to Stop Worrying and Love RAIDZ for details.

Note that the reference was written by one of the original ZFS authors and the main OpenZFS maintainer.

 

[Ericloewe]

Also, vdevs with more than 11 drives are a rather bad idea.