[OpenIndiana-discuss] moving existing rpool onto larger disks, in-place: zpool/zfs ashift/blocksize musings

[Bill Sommerfeld]

On 05/14/12 00:00, Hans J. Albertsson wrote:
> First: Can you ever efficiently migrate a zpool with ashift=9 to a 4k
> block disk by just adding the new disk as a 3rd mirror? Regardless of
> what blocksize the disk reports?

I butted heads with this yesterday, and concluded "no".

I attempted to moved a backup pool from an external USB enclosure to 
directly connected SATA, and it failed, with scary status messages from 
zpool import implying unrecoverable data corruption.

The pool was created with ashift=9, presumably because the USB enclosure 
presented a block size of 512.  The disks were "advanced format" disks 
with 4K physical sectors; I moved the disks back to the USB enclosure 
and the pool was fine.

> Third: How can one check to see what parameters (like ashift( a
> particular pool uses?

ashift is a property in the zfs volume label, which you can see with:

zdb -l /dev/dsk/c0t0d0s0

					- Bill