Hi Anand,
Nice work.
But I have some small questions about it.
Anand Jain wrote on 2015/11/09 18:56 +0800:
These set of patches provides btrfs hot spare and auto replace support
for you review and comments.
First, here below are the simple example steps to configure the same:
Add a spare device:
btrfs spare add /dev/sde -f
I'm sorry but I didn't quite see the benefit of a spare device.
Let's take the following example:
1) 2 RAID1 + 1 spare
(A + B) + C
2) 3 RAID1
(A + B + C)
Let's assume they are all 12G size, and there are 3 raid1 chunks.
Each one is 3G size.
In my understanding, in normal operation case:
For case 1), all raid chunks should only be allocated into 2 RAID disks,
and spare one should contains no raid1 chunks.
A B C
------ ------ ------
|free| |free| |free|
------ ------ | |
|3Ga1| |3Ga2| | |
------ ------ | |
|3Gb1| |3Gb2| | |
------ ------ | |
|3Gc1| |3Gc2| | |
------ ------ ------
For case 2), all raid1 chunks will be allocated into all 3 disks, making
the allocation more fair.
A B C
------ ------ ------
|free| |free| |free|
------ ------ ------
|free| |free| |free|
------ ------ ------
|3Gb2| |3Ga1| |3Ga2|
------ ------ ------
|3Gc1| |3Gc2| |3Gb1|
------ ------ ------
At least in normal operation case, case 1) makes device C useless, and
reduce the total usable space.
In disk B failure case:
For case 1), we can auto replace B with C.
And it will copy all data chunks from A to C.
Need to copy 9G data.
And after replace:
A B C
------ ------ ------
|free| | X | |free|
------ ------ ------
|3Ga1| | X |->|3Ga2|
------ ------ ------
|3Gb1| | X |->|3Gb2|
------ ------ ------
|3Gc1| | X |->|3Gc2|
------ ------ ------
For case 2), we can just relocate and recover the bad chunks in B.
It it should only need to copy 6G data.
And after the "recovery", it should be much the same as case 1):
A B C
------ ------ ------
|free| | X | |free|
------ ------ ------
|3Ga1|<\| X |/>|3Gc1|
------ ------ ------
|3Gb2| || X |/ |3Ga2|
------ ------ ------
|3Gc1| \| X | |3Gb1|
------ ------ ------
IIRC, the only benefit of a spare device is, we can ensure there is
enough space for a device place.(If the failing one is no larger than
spare).
But the cost is, increase in replace data copy and unfair chunk allocation.
So I am not sure if the cost is good enough for the case.
At least, enhancing the chunk relocation to fulfill the case 2) will
bring a much smaller code base.
Thanks,
Qu
OR if there is a spare device which is already added before the, just
run
btrfs dev scan [/dev/sde]
this 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
Thats it.
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
thread cycle the auto replace will pick the spare device (/dev/sde is
above example) to replace the failed device. And so the btrfs volume is
back to a healthy state.
Its btrfs 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.
No spare when device failed:
It would scan for spare device at the rate of transaction commit
and will trigger the auto replace when ever spare device is added.
Priority:
In some future work there can be some chronological order to pick
a spare and the failed device.
Patches:
Kernel:
First, it needs, Qu's per chunk missing device patchset,
which is part of the set here and also there is a light optimization
(patch 5/15) which was required as part of this enhancement.
Next patches 7,8/15 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.
Patch 9/15 fixes a bug where in we should have blocked the incompatible
feature at the device scan/add level instead/also at in the mount level.
This is because we don't have to bring a device into the device list,
if it is incompatible.
Next patches 10,11,12,13/15 adds support for Spare device. For the
details on how to add a spare device kindly see further below.
For kernel with out spare feature supported 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 14/15 provides function for auto replace, this is mainly
from the existing replace code, and in the long run I see opportunity
to merge these code with the replace code that is triggered from
the user spare.
Last 15/15, uses all these facilities, picks a failed device and
triggers a auto replace in a kthread (casualty_kthread())
Progs:
Would need 4 patches as listed below.
Known Bug:
As now I see below stale kmem cache during module unload. Which
I am digging.
------
BUG btrfs_path (Not tainted): Objects remaining in btrfs_path on
kmem_cache_close()
------
Anand Jain (10):
btrfs: optimize btrfs_check_degradable() for calls outside of barrier
btrfs: introduce device dynamic state transition to offline or failed
btrfs: check device for critical errors and mark failed
btrfs: block incompatible optional features at scan
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 for failed device and hot replace
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 | 7 +-
fs/btrfs/dev-replace.c | 116 ++++++++++++++++++++
fs/btrfs/dev-replace.h | 1 +
fs/btrfs/disk-io.c | 211 +++++++++++++++++++++++-------------
fs/btrfs/disk-io.h | 2 -
fs/btrfs/super.c | 20 +++-
fs/btrfs/transaction.c | 3 +-
fs/btrfs/volumes.c | 283 ++++++++++++++++++++++++++++++++++++++++++++++---
fs/btrfs/volumes.h | 27 +++++
9 files changed, 571 insertions(+), 99 deletions(-)
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