Date: Fri, 4 Jun 2010 13:09:43 +1000
From: Nick Piggin <npiggin@suse.de>
To: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Chris Mason <chris.mason@oracle.com>,
       James Bottomley <James.Bottomley@suse.de>,
       Matthew Wilcox <matthew@wil.cx>,
       Christof Schmitt <christof.schmitt@de.ibm.com>,
       Boaz Harrosh <bharrosh@panasas.com>, linux-scsi@vger.kernel.org,
       linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: Wrong DIF guard tag on ext2 write
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 <yq17hmhbmkb.fsf@sermon.lab.mkp.net>
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On Thu, Jun 03, 2010 at 09:46:02PM -0400, Martin K. Petersen wrote:
> >>>>> "Nick" == Nick Piggin <npiggin@suse.de> writes:
> 
> Nick> Also I don't think we can deal with memory errors and scribbles
> Nick> just by crcing dirty data. The calculations generating the data
> Nick> could get corrupted.
> 
> Yep, the goal is to make the window as small as possible.
> 
> 
> Nick> Data can be corrupted on its way back from the device to
> Nick> userspace.
> 
> We also get a CRC back from the storage.  So the (integrity-aware)
> application is also able to check on read.

Well that's nice :)


> Nick> Obviously this feature is being pushed by databases and such that
> Nick> really want to pass checksums all the way from userspace. Block
> Nick> retrying is _not_ needed or wanted here of course.
> 
> Nope.  The integrity error is bubbled all the way up to the database and
> we can decide to retry, recreate or error out depending on what we find
> when we do validation checks on the data buffer and the integrity
> metadata.

By block retrying, I just meant the bounce / re-checksum approach.

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