mirror_zfs/man/man8
Brian Behlendorf 6e91a72fe3
Disable 'zfs remap' command
The implementation of 'zfs remap' has proven to be problematic since
it modifies the objset (but not its logical contents) by dirtying
metadata without owning it.  The consequence of which is that
dmu_objset_remap_indirects() is vulnerable to certain races.

For example, if we are in the middle of receiving into the filesystem
while it is being remapped.  Then it is possible we could evict the
objset when the receive completes (see dsl_dataset_clone_swap_sync_impl,
or dmu_recv_end_sync), but dmu_objset_remap_indirects() may be still
using the objset.  The result of which would be a panic.

Extended runs of ztest(8) have exposed other possible races which
can occur when using 'zfs remap'.  Several of these have been fixed
but there may be others which have not yet been encountered and
diagnosed.

Furthermore, the ability to manually remap a filesystem is no longer
particularly useful now that the removal code can map large chunks.
Coupled with the fact that explaining what this command does and why
it may be useful requires a detailed understanding of the internals
of device removal.  These are details users should not be bothered
with.

Therefore, the 'zfs remap' command is being disabled but not entirely
removed.  It may be removed in the future or potentially reworked
to address the issues described above.  Since 'zfs remap' has never
been part of a tagged release its removal is expected to have
minimal impact.

The ZTS tests have been updated to continue to exercise the command
to prevent atrophy, but it has been removed entirely from ztest(8).

Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed by: Tom Caputi <tcaputi@datto.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #8238
2019-01-15 15:46:58 -08:00
..
.gitignore Ignore *.o.ur-safe build artifacts 2018-05-13 18:59:02 -07:00
fsck.zfs.8 Fix NAME section of manpages zhack and fsck.zfs. 2014-03-10 09:19:17 -07:00
Makefile.am Tunable directory for zfs runtime scripts 2018-06-07 09:59:59 -07:00
mount.zfs.8 zfs.8 & mount.zfs.8: fix a few typos 2016-05-16 12:26:31 -07:00
vdev_id.8 vdev_id support for device link aliases 2012-12-03 14:04:47 -08:00
zdb.8 OpenZFS 9166 - zfs storage pool checkpoint 2018-06-26 10:07:42 -07:00
zed.8.in Tunable directory for zfs runtime scripts 2018-06-07 09:59:59 -07:00
zfs-mount-generator.8.in Tunable directory for zfs runtime scripts 2018-06-07 09:59:59 -07:00
zfs-program.8 Add JSON output support to channel programs 2018-03-19 12:40:58 -07:00
zfs.8 Disable 'zfs remap' command 2019-01-15 15:46:58 -08:00
zgenhostid.8 Add mdoc style checker 2017-09-16 10:51:24 -07:00
zinject.8 OpenZFS 9403 - assertion failed in arc_buf_destroy() 2018-08-29 11:33:33 -07:00
zpool.8 Add 'zpool status -i' option 2019-01-07 11:03:18 -08:00
zstreamdump.8 Add zstreamdump(8) command to examine ZFS send streams. 2012-09-02 14:54:27 -07:00