Ucav's homelab blog

ThatGuyB · September 25, 2021, 2:32pm

ZFS has a default cluster size of 128KiB. You divide this by the number of drives in your vdev (not including parity) and you arrive at the amount of data written to each disk. Keep in mind that sectors on disks of this size are 4KiB, so you want your result to be a multiple of 4KiB or else you’ll have performance degradation.

Here are a few examples:
3-disk RAID-Z = 128KiB / 2 = 64KiB = good
4-disk RAID-Z = 128KiB / 3 = ~43KiB = BAD!
5-disk RAID-Z = 128KiB / 4 = 32KiB = good
9-disk RAID-Z = 128KiB / 8 = 16KiB = good
4-disk RAID-Z2 = 128KiB / 2 = 64KiB = good
5-disk RAID-Z2 = 128KiB / 3 = ~43KiB = BAD!
6-disk RAID-Z2 = 128KiB / 4 = 32KiB = good
10-disk RAID-Z2 = 128KiB / 8 = 16KiB = good
All this said, your configuration has introduced unfortunate constraints. Additionally, you did mention that performance isn’t extremely important

and some more discussions here ZFS RAID Config for old disks