A user reported on Bugzilla that they were seeing kernel BUGs when
attempting to replace a missing device on a RAID 6 array. After
identifying the apparent cause of the BUG, I reached the conclusion that
there wasn't a quick fix. Maybe Miao Xie can point something out that I
missed, as he originally implemented device replace on RAID 5/6 :)
Patch 4 has the details, but the main problem is that we can't create
bios for a missing device, so the main scrub code path isn't very
useful. On RAID 5/6, since we only have one mirror for any piece of
data, the missing device is the only mirror we can use. Clearly, (unless
I missed something), this case needs to be handled differently.
These patches are on top of v4.1-rc2. I ran the scrub and replace
xfstests and the script below, which also reproduces the original BUG.
Thanks!
Omar Sandoval (4):
Btrfs: remove misleading handling of missing device scrub
Btrfs: count devices correctly in readahead during RAID 5/6 replace
Btrfs: add RAID 5/6 BTRFS_RBIO_REBUILD_MISSING operation
Btrfs: fix device replace of a missing RAID 5/6 device
fs/btrfs/raid56.c | 87 +++++++++++++++++++++++++----
fs/btrfs/raid56.h | 10 +++-
fs/btrfs/reada.c | 4 +-
fs/btrfs/scrub.c | 164 +++++++++++++++++++++++++++++++++++++++++++++---------
4 files changed, 225 insertions(+), 40 deletions(-)
Testing script:
----
#!/bin/bash
USAGE="Usage: $0 [eio|missing] [raid0|raid1|raid5|raid6]"
if [ "$1" = "-h" ]; then
echo "$USAGE"
exit
fi
MODE="${1:-missing}"
RAID="${2:-raid5}"
case "$MODE" in
eio|missing)
;;
*)
echo "$USAGE" >&2
exit 1
;;
esac
case "$RAID" in
raid[0156])
;;
*)
echo "$USAGE" >&2
exit 1
;;
esac
NUM_DISKS=4
NUM_RAID_DISKS=3
SRC_DISK=1
TARGET_DISK=3
NUM_SECTORS=$((1024 * 1024))
LOOP_DEVICES=()
DM_DEVICES=()
cleanup () {
echo "Done. Press enter to cleanup..."
read
if findmnt /mnt; then
umount /mnt
fi
for DM in "${DM_DEVICES[@]}"; do
dmsetup remove "$DM"
done
for LOOP in "${LOOP_DEVICES[@]}"; do
losetup --detach "$LOOP"
done
for ((i = 0; i < NUM_DISKS; i++)); do
rm -f disk${i}.img
done
}
trap 'cleanup; exit 1' ERR
echo "Creating disk images..."
for ((i = 0; i < NUM_DISKS; i++)); do
rm -f disk${i}.img
dd if=/dev/zero of=disk${i}.img bs=512 seek=$NUM_SECTORS count=0
LOOP_DEVICES+=("$(losetup --find --show disk${i}.img)")
done
echo "Creating loopback devices..."
for LOOP in "${LOOP_DEVICES[@]}"; do
DM="${LOOP/\/dev\/loop/dm}"
dmsetup create "$DM" --table "0 $NUM_SECTORS linear $LOOP 0"
DM_DEVICES+=("$DM")
done
echo "Creating filesystem..."
FS_DEVICES=("${DM_DEVICES[@]:0:$NUM_RAID_DISKS}")
FS_DEVICES=("${FS_DEVICES[@]/#/\/dev\/mapper\/}")
MOUNT_DEVICE="${FS_DEVICES[$(((SRC_DISK + 1) % NUM_RAID_DISKS))]}"
mkfs.btrfs -d "$RAID" -m "$RAID" "${FS_DEVICES[@]}"
mount "$MOUNT_DEVICE" /mnt
cp -r ~/xfstests /mnt
sync
case "$MODE" in
eio)
echo "Killing disk..."
dmsetup suspend "${DM_DEVICES[$SRC_DISK]}"
dmsetup reload "${DM_DEVICES[$SRC_DISK]}" --table "0 $NUM_SECTORS error"
dmsetup resume "${DM_DEVICES[$SRC_DISK]}"
;;
missing)
echo "Removing disk and remounting degraded..."
umount /mnt
dmsetup remove "${DM_DEVICES[$SRC_DISK]}"
unset DM_DEVICES[$SRC_DISK]
mount -o degraded "$MOUNT_DEVICE" /mnt
;;
esac
echo "Replacing disk..."
btrfs replace start -B $((SRC_DISK + 1)) /dev/mapper/"${DM_DEVICES[$TARGET_DISK]}" /mnt
echo "Scrubbing to double-check..."
btrfs scrub start -Br /mnt
cleanup
----
--
2.4.0
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