Hi Neil,
Please consider the following scenario:
# degraded raid5 with 3 drives (A,B,C) and one missing
# a fresh drive D is added and starts rebuilding
# drive D fails
# after some time drive D is re-added
what happens is the following flow:
# super_1_validate does not set In_sync flag, because
MD_FEATURE_RECOVERY_OFFSET is set:
if ((le32_to_cpu(sb->feature_map) &
MD_FEATURE_RECOVERY_OFFSET))
rdev->recovery_offset = le64_to_cpu(sb->recovery_offset);
else
set_bit(In_sync, &rdev->flags);
rdev->raid_disk = role;
# As a result, add_new_disk does not set saved_raid_disk:
if (test_bit(In_sync, &rdev->flags))
rdev->saved_raid_disk = rdev->raid_disk;
else
rdev->saved_raid_disk = -1;
# then add_new_disk unconditionally does:
rdev->raid_disk = -1;
# Later remove_and_add_spares() resets rdev->recovery_offset and calls
the personality:
if (rdev->raid_disk < 0 && !test_bit(Faulty, &rdev->flags)) {
rdev->recovery_offset = 0;
if (mddev->pers->hot_add_disk(mddev, rdev) == 0) {
# And then raid5_add_disk does:
if (rdev->saved_raid_disk != disk)
conf->fullsync = 1;
which results in full sync.
This is on kernel 3.8.13, but your current for-linus branch has the
same issue, I believe.
Is this a reasonable behavior?
Also, I see that recovery_offset is basically not used at all during
re-add flow: we cannot resume the rebuild from recovery_offset,
because while the drive was out of the array, data may have been
written before recovery_offset, correct? That's why it is not used?
Thanks,
Alex.
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