Sector size of a zvol

Pete French petefrench at
Fri Feb 3 15:03:57 UTC 2012

> AFAIK, there is no way to specify the sector size to use in a ZFS pool: it
> is completely automatic when you call "zpool create". Ideally it should
> query the disk about its sector size and use that, but I don't know if
> that has been implemented (and can't be bothered to dig through the source
> at this time :).

I think we are talking about different things - the sector size used by
the zpool on the underlying system is automatic, and may or may not
come from the disc sector size (like you, I hope it does, but havent
checked ;-) ). But what I am talking about is the sector size
presneted by the 'fake' disc that a ZVOL creates - that always seems
to be 512 bytes, despite the fact that the zvol blocksize is 8k. Seems
odd to me (and that 8k size os alterable, but just doesnt seem to
be reflected in the zvol). As it stands I can make a zpool on top
of 4k discs, a ZVOL using 8k blocks on top of that, but the things
talking to it will use 512 byte chunks, which surely impacts performance ?


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