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

[Arne Jansen]

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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