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Re: Corrupted files

To: Eric Sandeen <sandeen@xxxxxxxxxxx>, Sean Caron <scaron@xxxxxxxxx>
Subject: Re: Corrupted files
From: Sean Caron <scaron@xxxxxxxxx>
Date: Tue, 9 Sep 2014 18:57:06 -0400
Cc: Leslie Rhorer <lrhorer@xxxxxxxxxxxx>, "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <540F7E37.7020500@xxxxxxxxxxx>
References: <540F1B01.3020700@xxxxxxxxxxxx> <CAA43vkXwHF9RHW-cbTZ91_vF6wiQ6o_+TQDL3=7kD9P4tErCNQ@xxxxxxxxxxxxxx> <CAA43vkWgh8-EjDXjkySUn+y18W1O+v_W5j+fQankRTgDCmc8tw@xxxxxxxxxxxxxx> <540F7E37.7020500@xxxxxxxxxxx>
Hey, just sharing some hard-won (believe me) professional experience. I have seen xfs_repair take a bad situation and make it worse many times. I don't know that a filesystem fuzzer or any other simulation can ever provide true simulation of users absolutely pounding the tar out of a system. There seems to be a real disconnect between what developers are able to test and observe directly, and what happens in the production environment in a very high-throughput environment.

Best,

Sean


On Tue, Sep 9, 2014 at 6:24 PM, Eric Sandeen <sandeen@xxxxxxxxxxx> wrote:
On 9/9/14 11:03 AM, Sean Caron wrote:

Barring rare cases, xfs_repair is bad juju.

No, it's not. It is the appropriate tool to use for filesystem repair.

But it is not the appropriate tool for recovery from mangled storage.

I've actually been running a filesystem fuzzer over xfs images, randomly
corrupting data and testing repair, 1000s of times over. It does
remarkably well.

If you scramble your raid, which means your block device is no longer
an xfs filesystem, but is instead a random tangle of bits and pieces of
other things, of course xfs_repair won't do well, but it's not the right
tool for the job at that stage.

-Eric

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