[zfs-discuss] recommendations for a 50 TB zpool?

Gordan Bobic gordan.bobic at gmail.com
Sun Nov 4 11:54:24 EST 2018


On Sun, 4 Nov 2018, 16:48 Richard Elling <richard.elling at richardelling.com
wrote:

>
> Note that random write I/O performance will be 120 IOPS per vdev (480 in
> first case, 240 in the other). It will be better for reads at approximately
> 720 and 300 respectively. Do some testing and maths to see whether that
> will suffice for your workload.
>
>
> You’ve got this backwards: raidz does well on random writes.
>

It always writes a full stripe - so it only gets 1 disk's worth of IOPS per
vdev. Regular parity raid typically get half of that because it requires
RMW for partial writes. RAIDZn does away with that by always writing a full
stripe.

It is the small, random read performance that suffers.
>

If no recovery is required, the "parity" disks are free to service the next
I/O required. So you get that part back in terms of IOPS.
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