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Re: Problem with file system on iSCSI FileIO

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: Problem with file system on iSCSI FileIO
From: Richard Sharpe <realrichardsharpe@xxxxxxxxx>
Date: Sat, 25 Sep 2010 10:14:05 -0700
Cc: Slawomir Nowakowski <slawomir.nowakowski@xxxxxxxxxx>, xfs@xxxxxxxxxxx
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On Sat, Sep 25, 2010 at 10:01 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> On Sat, Sep 25, 2010 at 09:54:46AM -0700, Richard Sharpe wrote:
>> fileio uses submit_bio to submit the data and it defaults to
>> WRITE_THROUGH, NV_CACHE and DIRECT_IO (at least in the trunk, but I
>> suspect this has been the case for a long while) however, the person
>> making the complaint might have switched off WRITE_THROUGH in the
>> pursuit of performance, in which case a crash could corrupt things
>> badly but it would depend on whether or not clearing WRITE_THROUGH
>> also clears NV_CACHE and what the code assembling the caching mode
>> page does (and I have only had a cursory glance at the vdisk code).
> If the target uses submit_bio for logical files inside a filesystems
> there are hundreds of ways to get exactly the corruption that Slawomir
> sees.  How does it obtain the logical to physical mapping?  What locking
> does it use agains other access to the file?

Actually, I was wrong. for fileio it does vfs_writev. I started
wondering the same questions and went back through the code and
noticed that I had missed a test.

We really need to know what parameters the person making the complaint
is using, and the version of SCST.

In addition, I don't understand when this corruption occurred ...

It really might be a case of don't do that.

Richard Sharpe

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