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Date: Thu, 05 Jun 2014 11:27:12 +0200
From: Peter Lieven <pl@kamp.de>
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Subject: Re: [Qemu-devel] [PATCH] block/iscsi: use 16 byte CDBs only when
 necessary
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To: Michael Tokarev <mjt@tls.msk.ru>, ronnie sahlberg <ronniesahlberg@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, qemu-devel <qemu-devel@nongnu.org>, Stefan Hajnoczi <stefanha@redhat.com>

On 05.06.2014 11:12, Michael Tokarev wrote:
> 04.06.2014 18:00, ronnie sahlberg wrote:
>> That would mean you get to use the 10 version of the cdb even for very
>> large devices (as long as the IO is for blocks at the beginning of the
>> device) and thus provide partial avoidance of this issue for those
>> large devices.
> That may make some bugs "ghosty", so to say.  Ie, if there's a bug in/with
> 16 version of a command, you'll hit it only when you actually try to access
> a "far" area of a drive.  Which means you're unlikely to hit it while trying
> to reproduce in a clean environment, even after using a large device.  Or,
> the bug will be triggered at random, since data placement on the filesystem
> is effectively (from user PoV) random.
>
> To my taste it is better to make it a bit more deterministic.

Yes, that was my fear as well. We make the decision for the whole target
if 48bit adressing is needed, we use 16 Byte CDBs for all requests independend
of the LBA offset.

Peter

>
> Thanks,
>
> /mjt