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    SubjectRe: [patch 4/5] fail-injection capability for disk IO
    On Wed, 23 Aug 2006 14:03:55 +0200
    Jens Axboe <axboe@suse.de> wrote:

    > On Wed, Aug 23 2006, Akinobu Mita wrote:
    > > This patch provides fail-injection capability for disk IO.
    > >
    > > Boot option:
    > >
    > > fail_make_request=<probability>,<interval>,<times>,<space>
    > >
    > > <probability>
    > >
    > > specifies how often it should fail in percent.
    > >
    > > <interval>
    > >
    > > specifies the interval of failures.
    > >
    > > <times>
    > >
    > > specifies how many times failures may happen at most.
    > >
    > > <space>
    > >
    > > specifies the size of free space where disk IO can be issued
    > > safely in bytes.
    > >
    > > Example:
    > >
    > > fail_make_request=100,10,-1,0
    > >
    > > generic_make_request() fails once per 10 times.
    >
    > Hmm dunno, seems a pretty useless feature to me.

    We need it. What is the FS/VFS/VM behaviour in the presence of IO
    errors? Nobody knows, because we rarely test it. Those few times where
    people _do_ test it (the hard way), bad things tend to happen. reiserfs
    (for example) likes to go wobble, wobble, wobble, BUG.

    > Wouldn't it make a lot
    > more sense to do this per-queue instead of a global entity?

    Yes, I think so. /sys/block/sda/sda2/make-it-fail.

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