zfs ashift

<gotwf> poiuty: ashift=9 if you're unconcerned with adding additional drives that may have larger sectors.
<poiuty> gotwf: what about perfomance? It`s 2 disk to mirror
<gotwf> poiuty: ashift=9 will be better tuned for what you actually have, ashift=12 for what you may yet get.  In such instances I tend to optimize for what I have to today and am quite likely to have tomorrow, and not get too caught up in what I may need next week.
<gotwf> poiuty: ashift=9 will be less "wasted" space.  I'm using ashift=9 on my 512K drives.

<gotwf> Uh... 512b
<gotwf> ashift=12 would be better perf IF you had 4K drives.
or if you ever wanted to integrate 4k drives into the same pool later

I recommend always, always, always using ashift 12 because you can't change it after creation. Even if you have 512-byte disks now, eventually you are likely to replace failed disks with 4K ones. Unless you are sure it would be no problem to recreate your array, then just go ashift 12 now.