Re: iSCSI Expected Data Transfer Length for T10-PI

[Sagi Grimberg <sagig@dev.mellanox.co.il>]

On 5/27/2014 2:58 PM, Black, David wrote:
> Hi Sagi,

Hey David,

>
>> RFC-7143 states:
>> "the Expected Data Transfer Length field contains the number of bytes of
>> data involved in this SCSI operation."
>> Since this field relates to *data bytes* I kept T10-PI implicit wrt this
>> field. The iSCSI target calculates the
>> total transfer length (data + protection) from the cdb transfer length
>> field and protect bits.
> That is wrong.  At the SCSI transport interface (both iSCSI and FCP are
> SCSI transports), the concept of "data bytes" includes SCSI protection
> information.
>
>> In FC, the fc_dl field was updated to relate to the total number of
>> transfer bytes and includes
>> data and protection bytes. virtio_scsi was added with a header PI
>> section (virtio_scsi_cmd_req_pi).
> That is the correct approach.
>
> At the SCSI transport interface (both FCP and iSCSI are SCSI transports),
> no distinction is made between user data and protection information.
> therefore, a transfer of 512 bytes of user data + 8 bytes of protection
> information is a 520 byte transfer for both protocols.
>
> The authority for this is SAM-5, or SAM-4 if one wants to refer to an
> approved standard.  Neither are open to interpretation on this point.

I see, thanks for clarifying this for me.

> All SCSI transports are supposed to behave the same way.  I hope this
> can be corrected quickly.

No problem, I'll fix it.

Sagi.