vdevs with different spindle speeds

Mel Pilgrim list_freebsd at bluerosetech.com
Sat Dec 5 13:24:53 UTC 2020

On 2020-12-05 4:38, tech-lists wrote:
> Normally when making an array, I'd like to use all disks all same speed,
> interface, make and model but from different batches. In this case, I've no
> choice, so we have multiple 1TB disks some 7.2k some 5.4k. I've not mixed
> them like this before.
> What effect would this have on the final array? Slower than if all one or the other?
> No effect? I'm expecting the fastest access will be that of the slowest vdev.
> Similarly some disks block size is 512b logical/512b physical, others are 512b
> logical/4096 physical, still others are 4096/4096. Any effect of
> mixing hardware? I understand zfs sets its own blocksize.

Make sure you have ashift=12 for everything and you'll be fine.  The 
marginal increase in latency with the 5400 rpm drives will disappear 
behind ZFS' heavily-cached, asynchronous operation unless you're 
hammering the pool with calls for cold data.

If you're really worried about it, get a cheap SSD and use it as a cache 

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