The patchset can be fetched from my github repo:
https://github.com/adam900710/linux/tree/degradable
The patchset is based on David's for-4.13-part1 branch.
Btrfs currently uses num_tolerated_disk_barrier_failures to do global
check for tolerated missing device.
Although the one-size-fit-all solution is quite safe, it's too strict
if data and metadata has different duplication level.
For example, if one use Single data and RAID1 metadata for 2 disks, it
means any missing device will make the fs unable to be degraded
mounted.
But in fact, some times all single chunks may be in the existing
device and in that case, we should allow it to be rw degraded mounted.
Such case can be easily reproduced using the following script:
# mkfs.btrfs -f -m raid1 -d sing /dev/sdb /dev/sdc
# wipefs -f /dev/sdc
# mount /dev/sdb -o degraded,rw
If using btrfs-debug-tree to check /dev/sdb, one should find that the
data chunk is only in sdb, so in fact it should allow degraded mount.
This patchset will introduce a new per-chunk degradable check for
btrfs, allow above case to succeed, and it's quite small anyway.
And enhance kernel error message for missing device, at least user
can know what's making mount failed, other than meaningless
"failed to read system chunk/chunk tree -5".
v2:
Update after almost 2 years.
Add the last patch to enhance the kernel output, so user can know
it's missing devices that prevents btrfs to be mounted.
v3:
Remove one duplicated missing device output
Use the advice from Anand Jain, not to add new members in btrfs_device,
but use a new structure extra_rw_degrade_errors, to record error when
sending down/waiting device.
v3.1:
Reduce the critical section in btrfs_check_rw_degradable(), follow other
caller to only acquire the lock when searching, as extent_map has
refcount to avoid concurrency already.
The modification itself won't affect the behavior, so tested-by tags are
added to each patch.
v4:
Thanks Anand for this dev flush work, which makes us more easier to
detect flush error in previous transaction.
Now this patchset won't need to alloc memory, and can just use
btrfs_device->last_flush_error to check if last flush finished
correctly.
New rebase, so old tested by tags are all removed, sorry guys.
Qu Wenruo (6):
btrfs: Introduce a function to check if all chunks a OK for degraded
rw mount
btrfs: Do chunk level rw degrade check at mount time
btrfs: Do chunk level degradation check for remount
btrfs: Allow barrier_all_devices to do chunk level device check
btrfs: Cleanup num_tolerated_disk_barrier_failures
btrfs: Enhance missing device kernel message
fs/btrfs/ctree.h | 2 --
fs/btrfs/disk-io.c | 81 ++++----------------------------------------
fs/btrfs/disk-io.h | 2 --
fs/btrfs/super.c | 3 +-
fs/btrfs/volumes.c | 99 +++++++++++++++++++++++++++++++++++++++++-------------
fs/btrfs/volumes.h | 3 ++
6 files changed, 85 insertions(+), 105 deletions(-)
--
2.13.1
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