On 10/18/11 03:31 PM, Tim Cook wrote:

On Tue, Oct 18, 2011 at 3:27 PM, Peter Tribble <peter.trib...@gmail.com <mailto:peter.trib...@gmail.com>> wrote:

    On Tue, Oct 18, 2011 at 9:12 PM, Tim Cook <t...@cook.ms
    <mailto:t...@cook.ms>> wrote:
    > On Tue, Oct 18, 2011 at 3:06 PM, Peter Tribble
    <peter.trib...@gmail.com <mailto:peter.trib...@gmail.com>>
    > wrote:
    >> On Tue, Oct 18, 2011 at 8:52 PM, Tim Cook <t...@cook.ms
    <mailto:t...@cook.ms>> wrote:
    >> >
    >> > Every scrub I've ever done that has found an error required
    >> > fixing.
    >> >  Every pool I've ever created has been raid-z or raid-z2, so
    the silent
    >> > healing, while a great story, has never actually happened in
    practice in
    >> > any
    >> > environment I've used ZFS in.
    >> You have, of course, reported each such failure, because if that
    >> was indeed the case then it's a clear and obvious bug?
    >> For what it's worth, I've had ZFS repair data corruption on
    >> several occasions - both during normal operation and as a
    >> result of a scrub, and I've never had to intervene manually.
    >> --
    >> -Peter Tribble
    >> http://www.petertribble.co.uk/ - http://ptribble.blogspot.com/
    > Given that there  are guides on how to manually fix
    the corruption, I don't
    > see any need to report it.  It's considered acceptable and
    expected behavior
    > from everyone I've talked to at Sun...
    > http://dlc.sun.com/osol/docs/content/ZFSADMIN/gbbwl.html

    If you have adequate redundancy, ZFS will - and does -
    repair errors. The document you quote is for the case
    where you don't actually have adequate redundancy: ZFS
    will refuse to make up data for you, and report back where
    the problem was. Exactly as designed.

    (And yes, I've come across systems without redundant
    storage, or had multiple simultaneous failures. The original
    statement was that if you have redundant copies of the data
    or, in the case of raidz, enough information to reconstruct
    it, then ZFS will repair it for you. Which has been exactly in
    accord with my experience.)

    -Peter Tribble
    http://www.petertribble.co.uk/ - http://ptribble.blogspot.com/

I had and have redundant storage, it has *NEVER* automatically fixed it. You're the first person I've heard that has had it automatically fix it. Per the page "or an unlikely series of events conspired to corrupt multiple copies of a piece of data."

Their unlikely series of events, that goes unnamed, is not that unlikely in my experience.

Just another 2 cents towards a euro/dollar/yen. I've only had data redundancy in ZFS via mirrors (not that it should matter as long as there's redundancy), and in every case I've had it repair data automatically via a scrub. The one case where it didn't was when the disk controller both drives happened to share (bad design, yes) started erroring and corrupting writes to both disks in parallel, so there was no good data to fix it with. I was still happy to be using ZFS, as a filesystem without a scrub/scan of some sort wouldn't have even noticed in my experience - I suspect btrfs would have if it's scan works similarly.


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Brian Wilson, Solaris SE, UW-Madison DoIT
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