getting to 4K disk blocks in ZFS

[Peter Wemm]

On Wednesday, September 10, 2014 04:46:28 PM Aristedes Maniatis wrote:
> As we all know, it is important to ensure that modern disks are set up
> properly with the correct block size. Everything is good if all the disks
> and the pool are "ashift=9" (512 byte blocks). But as soon as one new drive
> requires 4k blocks, performance drops through the floor of the enture pool.
[..]
> And secondly, is it also bad to have ashift 9 disks inside a ashift 12 pool?
> That is, do we need to replace all our disks in one go and forever keep big
> sticky labels on each disk so we never mix them?

For what its worth, in the freebsd.org cluster we automatically align 
everything to a minimum of 4k, no matter what the actual drive is.

We set:  sysctl vfs.zfs.min_auto_ashift=12
(this saves a lot of messing around with gnop etc)

and ensure all the gpt slices are 4k or better aligned.

-- 
Peter Wemm - peter at wemm.org; peter at FreeBSD.org; peter at yahoo-inc.com; KI6FJV
UTF-8: for when a ' or ... just won\342\200\231t do\342\200\246
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