Sector size of a zvol

David Magda dmagda at
Fri Feb 3 15:47:26 UTC 2012

On Fri, February 3, 2012 10:03, Pete French wrote:
> [...] 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 ?

Try the following from the zfs(1M) man page:

    zfs create [-ps] [-b blocksize] [-o property=value] ... -V size volume
	 -b blocksize

	   Equivalent to -o  volblocksize=blocksize.  If  this  option  is
	   specified  in  conjunction  with -o volblocksize, the resulting
	   behavior is undefined.

Did use "blocksize" or "volblocksize" in your "zfs create" command?

A thread for zfs-discus on "volblocksize":

More information about the freebsd-stable mailing list