On 05/28/12 17:13, Daniel Carosone wrote:
There are two problems using ZFS on drives with 4k sectors:
1) if the drive lies and presents 512-byte sectors, and you don't
manually force ashift=12, then the emulation can be slow (and
possibly error prone). There is essentially an internal RMW cycle
when a 4k sector is partially updated. We use ZFS to get away
from the perils of RMW :)
2) with ashift=12, whther forced manually or automatically because
the disks present 4k sectors, ZFS is less space-efficient for
metadata and keeps fewer historical uberblocks.
two, more specific, problems I've run into recently:
1) if you move a disk with an ashift=9 pool on it from a
controller/enclosure/.. combo where it claims to have 512 byte sectors
to a path where it is detected as having 4k sectors (even if it can cope
with 512-byte aligned I/O), the pool will fail to import and appear to
be gravely corrupted; the error message you get will make no mention of
the sector size change. Move the disk back to the original location and
it imports cleanly.
2) if you have a pool with ashift=9 and a disk dies, and the intended
replacement is detected as having 4k sectors, it will not be possible to
attach the disk as a replacement drive..
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