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draid: fix cksum errors after rebuild with degraded disks

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Currently, when more than nparity disks get faulted during the
rebuild, only first nparity disks would go to faulted state, and
all the remaining disks would go to degraded state. When a hot
spare is attached to that degraded disk for rebuild creating the
spare mirror, only that hot spare is getting rebuilt, but not the
degraded device. So when later during scrub some other attached
draid spare happens to map to that spare, it will end up with
cksum error.

Moreover, if the user clears the degraded disk from errors, the
data won't be resilvered to it, hot spare will be detached almost
immediately and the data that was resilvered only to it will be
lost.

Solution: write to all mirrored devices during rebuild, similar
to traditional/healing resilvering, but only if we can verify
the integrity of the data, or when it's the draid spare we are
writing to, in which case we are writing to a reserved spare
space, and there is no danger to overwrite any good data.

The argument that writing only to rebuilding draid spare vdev is
faster than writing to normal device doesn't hold since, at a
specific offset being rebuilt, draid spare will be mapped to a
normal device anyway.

redundancy_draid_degraded2 automation test is added also to
cover the scenario.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Andriy Tkachuk <atkachuk@wasabi.com>
Closes #18414
This commit is contained in:
Andriy Tkachuk
2026-04-15 22:48:00 +01:00
committed by Tony Hutter
parent eec8b9b929
commit da44040bbb
8 changed files with 235 additions and 19 deletions
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module/zfs/vdev_mirror.c
+7 -11
View File
@@ -669,23 +669,19 @@ vdev_mirror_io_start(zio_t *zio)
}
while (children--) {
mc = &mm->mm_child[c];
c++;
mc = &mm->mm_child[c++];
/*
* When sequentially resilvering only issue write repair
* IOs to the vdev which is being rebuilt for two reasons:
* 1. The repair IO data calculated from parity has no checksum
* to validate and could be incorrect. Existing data must
* never be overwritten with unconfirmed data to ensure we
* never lock in unrecoverable damage to the pool.
* 2. Performance is limited by the slowest child device. We
* don't want a slower device to limit the rebuild rate for
* faster replacement devices such as distributed spares.
* When sequentially resilvering and the integrity of the data
* is speculative (ZIO_FLAG_SPECULATIVE), issue write repair IOs
* only to the vdev which is being rebuilt. Existing data on
* other children must never be overwritten with unconfirmed
* data to avoid unrecoverable damage to the pool.
*/
if ((zio->io_priority == ZIO_PRIORITY_REBUILD) &&
(zio->io_flags & ZIO_FLAG_IO_REPAIR) &&
!(zio->io_flags & ZIO_FLAG_SCRUB) &&
(zio->io_flags & ZIO_FLAG_SPECULATIVE) &&
mm->mm_rebuilding && !mc->mc_rebuilding) {
continue;
}