linux-kernel - Re: [PATCH v5 0/3] Btrfs: add IO error device stats

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Date:	Fri, 25 May 2012 22:41:34 +0200
From:	Arne Jansen <sensille@....net>
To:	Stefan Behrens <sbehrens@...ntdisaster.de>
CC:	Christoph Hellwig <hch@...radead.org>, linux-btrfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/3] Btrfs: add IO error device stats

On 05/25/12 19:49, Stefan Behrens wrote:
> It would be helpful if already the generic block layer would offer
> device error counters. Then btrfs could read them, add own counters for
> its checksum detected errors, and store everything persistently in the
> filesystem.
>

I take it that you not only count I/O-errors, but also corrupted blocks
and errors generated by misdirected writes. These are informations that
are not available to the block layer.


> The goal is to replace disks that have an increased error rate with
> spare disks, and the goal is to repair this degenerated RAID state quickly.
>
>
> On 05/25/2012 17:18, Christoph Hellwig wrote:
>> Can you explain why the device error counters should be in a filesystem
>> instead of generic block layer code?
>>
>> On Fri, May 25, 2012 at 04:06:07PM +0200, Stefan Behrens wrote:
> [...]
>>> The goal is to detect when drives start to get an increased error rate,
>>> when drives should be replaced soon. Therefore statistic counters are
>>> added that count IO errors (read, write and flush). Additionally, the
>>> software detected errors like checksum errors and corrupted blocks are
>>> counted.
>>>
>>> An ioctl interface is added to get the device statistic counters.
>>> A second ioctl is added to atomically get and reset these counters.
>>>
>>> The device statistics are written into the device tree with each
>>> transaction commit. Only modified statistics are written.
>>> When a filesystem is mounted, the device statistics for each involved
>>> device are read from the device tree and used to initialize the
>>> counters.
>>>
>>> A patch for the btrfs-progs world will also be sent.
>>>
>>> Stefan Behrens (3):
>>> Btrfs: add device counters for detected IO and checksum errors
>>> Btrfs: add ioctl to get and reset the device stats
>>> Btrfs: read device stats on mount, write modified ones during commit
>>>
>>> fs/btrfs/ctree.h | 38 ++++++
>>> fs/btrfs/disk-io.c | 20 +++-
>>> fs/btrfs/extent_io.c | 18 ++-
>>> fs/btrfs/ioctl.c | 26 +++++
>>> fs/btrfs/ioctl.h | 33 ++++++
>>> fs/btrfs/print-tree.c | 3 +
>>> fs/btrfs/scrub.c | 65 ++++++++---
>>> fs/btrfs/transaction.c | 4 +
>>> fs/btrfs/volumes.c | 304
>>> +++++++++++++++++++++++++++++++++++++++++++++++-
>>> fs/btrfs/volumes.h | 52 +++++++++
>>> 10 files changed, 539 insertions(+), 24 deletions(-)
>>>
>>> --
>>> 1.7.10.2
> --
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