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Date: Tue, 17 Jun 2014 13:37:11 +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: Paolo Bonzini <pbonzini@redhat.com>, Michael Tokarev <mjt@tls.msk.ru>, ronnie sahlberg <ronniesahlberg@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-devel <qemu-devel@nongnu.org>, Stefan Hajnoczi <stefanha@redhat.com>

On 17.06.2014 13:15, Paolo Bonzini wrote:
> Il 17/06/2014 08:14, Peter Lieven ha scritto:
>>>
>>
>> BTW, while debugging a case with a bigger storage supplier I found
>> that open-iscsi seems to do exactly this undeterministic behaviour.
>> I have a 3TB LUN. If I access < 2TB sectors it uses READ10/WRITE10 and
>> if I go beyond 2TB it changes to READ16/WRITE16.
>
> Isn't that exactly what your latest patch does for >64K sector writes? :)

Not exactly, we choose the default by checking the LUN size. 10 Byte for < 2TB and
16 Byte otherwise.

My latest patch makes an exception if a request is bigger than 64K sectors and
switches to 16 Byte requests. These would otherwise end in an I/O error.

open-iscsi uses 10 Byte requests for any sector offset smaller than 2^32 regardless
of the LUN size and 16 Byte requests otherwise.

Peter

>
> It's the reason why I haven't merged that patch yet.
>
> Paolo


-- 

Mit freundlichen Grüßen

Peter Lieven

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