Thanks for various comments, tests and feedback.
Background: Hot spare and Auto replace:
Hot spare is predominately used to mitigate or narrow the time
window of a storage in degraded mode during which any further disk
failure might lead to a catastrophic data loss. Data center
storage generally will have couple of disks reserved as spares
on the storage. Mainly this is an enterprise storage feature
rather than a FS feature, I believe people acquainted with
enterprise storage use cases will appreciate the need of it and
so most/all of the enterprise storage has hot spare feature.
Btrfs device states:
This patch-set adds 'failed' state and makes provision to use
'offline' state as two new device states. So to summarize
various device states and their meanings..
/* missing: device wasn't found at the time of mount */
int missing;
/*
* failed: device confirmed to have experienced critical
* io failure
*/
int failed;
/*
* offline: When there is no confirmation that a disk has
* failed. But an interim communication breakdown
* and not necessarily a candidate for the device replace.
* Device might be online after user intervention or after
* block transport layer error recovery.
*/
int offline;
Device state transition Tuning and visualization:
Sysfs interfaces are planned to provide the required tuning for
device state transition sensitivities and visualization of device
states. However sysfs framework which could provide such an interface
is being reviewed/tested and not yet ready as of now. So for the
testing and debug of these features here I have used an update
version of the procfs patch which is in the ML.
[PATCH] btrfs: debug: procfs-devlist: introduce procfs interface for
the device list for debugging
I find the above patch very useful and stable as compared to sysfs
to visualize the device state.
This patch set does not depend on any of the sysfs patches as such.
Cross compatibility:
Adds a new incompatibility feature flags
(BTRFS_FEATURE_INCOMPAT_SPARE_DEV) to manage the spare device
when older kernels are used. So it is tested to be work fine
with older kernel/prog versions.
Auto replace:
Replace happens automatically, that is when there is any write
failed or flush failed, the device will be marked as failed, which
will stop any further IO attempt to that device. And in the next
commit cycle the auto replace will pick the spare device to
replace the failed device. And so the btrfs volume is back to a
healthy state.
Per FSID spare vs Global spare:
As of now only global hot spare is supported, that is hot spare(s)
are for all the btrfs FS in the system. However future there will
be a fs_info->no_auto_replace tunable which can be tuned by the user
to limit the use of global spare.
Example use case:
Here below is an example use case of the hot spare setup.
Add a spare device:
btrfs spare add /dev/sde -f
If there is a spare device which is already added before the,
just run
btrfs dev scan [/dev/sde]
Which will register the spare device to the kernel.
btrfs fi show
Label: none uuid: 52f170c1-725c-457d-8cfd-d57090460091
Total devices 2 FS bytes used 112.00KiB
devid 1 size 2.00GiB used 417.50MiB path /dev/sdc
devid 2 size 2.00GiB used 417.50MiB path /dev/sdd
Global spare
device size 3.00GiB path /dev/sde
Patches:
Kernel:
First, it needs, Qu's per chunk missing device patchset, which is
part of the set.
Next patches 6/12 brings in support to manage the transition of
devices from online (no state) to offline OR failed state dynamically.
On top of static device state like the current "missing" state.
Next patches 7-11/12 adds support for Spare device. For kernel without
spare feature the spare device is kept away. And when the kernel
supports the spare device, it will inhibit from mounting it. Further
these patch set provides helper function to pick a spare device and
release a spare device back to the spare device pool.
Patch 11/12 provides function for auto replace, this is mainly
from the existing replace code.
Last 12/15, uses all these facilities, picks a failed device and
triggers a auto replace in a kthread (casualty_kthread())
Progs:
Needs below 4 patches which will add sub cli 'spare' to manage
the spare device. As of now deleting a spare device has to be
managed using wipefs. However in the long run we would a proper
btrfs command to do that job.
V1->V2:
Kernel:
(Based on tests and commets provided in the ML)
a. Now transition_kthread() wakes up the casualty_kthread to check
for device states. Instead of doing that in the transition_kthread()
itself. Cleaner and less pressure on transition_kthread().
b. Dropped
[PATCH 05/15] btrfs: optimize btrfs_check_degradable() for calls outside
of barrier
as it was wrong patch and the optimization was incomplete.
c. Merged patches
btrfs: check for failed device and hot replace
to
btrfs: check device for critical errors and mark failed
in an effort to make the changes as in a above.
Progs:
a. Added to call btrfs_register_one_device() when doing btrfs
spare add
Anand Jain (7):
btrfs: introduce device dynamic state transition to offline or failed
btrfs: introduce BTRFS_FEATURE_INCOMPAT_SPARE_DEV
btrfs: add check not to mount a spare device
btrfs: support btrfs dev scan for spare device
btrfs: provide framework to get and put a spare device
btrfs: introduce helper functions to perform hot replace
btrfs: check device for critical errors and mark failed
Qu Wenruo (5):
btrfs: Introduce a new function to check if all chunks a OK for
degraded mount
btrfs: Do per-chunk check for mount time check
btrfs: Do per-chunk degraded check for remount
btrfs: Allow barrier_all_devices to do per-chunk device check
btrfs: Cleanup num_tolerated_disk_barrier_failures
fs/btrfs/ctree.h | 8 +-
fs/btrfs/dev-replace.c | 24 +++++
fs/btrfs/dev-replace.h | 1 +
fs/btrfs/disk-io.c | 256 +++++++++++++++++++++++++++++++++--------------
fs/btrfs/disk-io.h | 4 +-
fs/btrfs/super.c | 20 +++-
fs/btrfs/volumes.c | 263 +++++++++++++++++++++++++++++++++++++++++++++----
fs/btrfs/volumes.h | 27 +++++
8 files changed, 504 insertions(+), 99 deletions(-)
Anand Jain (4):
btrfs-progs: Introduce BTRFS_FEATURE_INCOMPAT_SPARE_DEV SB flags
btrfs-progs: Introduce btrfs spare subcommand
btrfs-progs: add fi show for spare
btrfs-progs: add global spare device list to filesystem show
Android.mk | 2 +-
Makefile.in | 3 +-
btrfs.c | 1 +
cmds-filesystem.c | 9 ++
cmds-spare.c | 292 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
commands.h | 2 +
ctree.h | 4 +-
utils.h | 1 +
volumes.c | 4 +
volumes.h | 2 +
10 files changed, 317 insertions(+), 3 deletions(-)
create mode 100644 cmds-spare.c
--
2.7.0
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