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    SubjectRe: Pe: [PATCH v5 1/3] virtio-scsi: first version
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    Hello Paolo,

    On 07/02/12 13:31, Paolo Bonzini wrote:
    > The structure of the LUN is defined by SAM, not by me.

    Just had a look at the SAM LUN structure. It appears that you are using
    the SCSI format for hierarchical LUNs(SAM 5 chapter 4.7.6) in order to
    indicate that the LUN is actually attached to the host system and not to
    the Qemu guest operating system itself.

    What I am wondering is why you are doing this? The hierarchical SCSI
    format is only retained while the LUN number is being transmitted over the
    virtqueue, so there does not seem to be a technical necessity for using
    this format in order to transmit SCSI target ID and LUN number information
    to the host.

    Instead the format has some disadvantages:
    - It uses up 8 bytes where 3 bytes would be sufficient in order to store
    both the target ID and LUN number information
    - The format limits us to 255 target IDs. I agree that the LUN limit is
    probably more a theoretical and not a practical one, but 255 target IDs
    could become a limitation in the future.

    Nonetheless I think that virtio-scsi is a useful project and addresses
    many of the limitations imposed by virtio-block. The fact that I am still
    persisting has more to do with interest in the project rather than wanting
    to keep the code from going upstream. Thank you for your work on this
    topic.

    Mit freundlichen Grüßen / Kind regards

    Christian Hoff

    Student - Applied Computer Science


    Phone:
    49-16098976-950
    IBM Deutschland

    E-Mail:
    christian.hoff@de.ibm.com
    Am Fichtenberg 1


    71083 Herrenberg


    Germany


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    Geschäftsführung: Martina Koederitz (Vorsitzende), Reinhard Reschke,
    Dieter Scholz, Gregor Pillen, Joachim Heel, Christian Noll
    Sitz der Gesellschaft: Ehningen / Registergericht: Amtsgericht Stuttgart,
    HRB 14562 / WEEE-Reg.-Nr. DE 99369940




    From:
    BORNTRAE@linux.vnet.ibm.com
    To:
    Paolo Bonzini <pbonzini@redhat.com>
    Cc:
    Christian Hoff/Germany/IBM@IBMDE, linux-kernel@vger.kernel.org,
    linux-scsi@vger.kernel.org, rusty@rustcorp.com.au, mst@redhat.com,
    kvm@vger.kernel.org
    Date:
    07/02/2012 14:18
    Subject:
    Re: Pe: [PATCH v5 1/3] virtio-scsi: first version



    On 07/02/12 13:31, Paolo Bonzini wrote:
    > The structure of the LUN is defined by SAM, not by me.

    Ok, got it.



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