diff options
| author | Martin Matuska <[email protected]> | 2013-04-12 10:26:03 -0700 |
|---|---|---|
| committer | Brian Behlendorf <[email protected]> | 2013-04-12 10:50:46 -0700 |
| commit | b28e57cb82c5d5a992b90c56f67dd7dbf9b6f296 (patch) | |
| tree | f2e2e84de3d437c24454b27ed69706c9260ddf4c /module/zfs/vdev.c | |
| parent | 295304bed6fa6744b8d011e36b9c2180311cedb2 (diff) | |
Allow setting a lower ashift with -o ashift
Previous patches have allowed you to set an increased ashift to
avoid doing 512b IO with 4k sector devices. However, it was not
possible to set the ashift lower than the reported physical sector
size even when a smaller logical size was supported. In practice,
there are several cases where settong a lower ashift is useful:
* Most modern drives now correctly report their physical sector
size as 4k. This causes zfs to correctly default to using a 4k
sector size (ashift=12). However, for some usage models this
new default ashift value causes an unacceptable increase in
space usage. Filesystems with many small files may see the
total available space reduced to 30-40% which is unacceptable.
* When replacing a drive in an existing pool which was created
with ashift=9 a modern 4k sector drive cannot be used. The
'zpool replace' command will issue an error that the new drive
has an 'incompatible sector alignment'. However, by allowing
the ashift to be manual specified as smaller, non-optimal,
value the device may still be safely used.
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #1381
Closes #1328
Issue #967
Issue #548
Diffstat (limited to 'module/zfs/vdev.c')
| -rw-r--r-- | module/zfs/vdev.c | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/module/zfs/vdev.c b/module/zfs/vdev.c index 06097f355..afff4d423 100644 --- a/module/zfs/vdev.c +++ b/module/zfs/vdev.c @@ -1258,11 +1258,12 @@ vdev_open(vdev_t *vd) if (vd->vdev_asize == 0) { /* * This is the first-ever open, so use the computed values. - * For testing purposes, a higher ashift can be requested. + * For compatibility, a different ashift can be requested. */ vd->vdev_asize = asize; vd->vdev_max_asize = max_asize; - vd->vdev_ashift = MAX(ashift, vd->vdev_ashift); + if (vd->vdev_ashift == 0) + vd->vdev_ashift = ashift; } else { /* * Detect if the alignment requirement has increased. |