RE: A question on Zero Copy

["Y P Cheng" <ycheng@advansys.com>]

> From: Douglas Otis [mailto:dotis@sanlight.net]
> Sent: Wednesday, December 06, 2000 2:03 PM
>
> Y.P.
>
> In Julian's defense, I suspect most targets will be dedicated appliances
> where memory handling is specialized to the point of not being influenced
> greatly by discontinuities created in blind placement of
> segments.  I doubt
> there is anything within the protocol that would allow a target advanced
> knowledge of segment content.  Otherwise, you are right about needing
> content directed zero copy witin the target as well.
>
> Doug

I believe you are referring to disk and tape drives as "dedicated
appliances".  In such context you are totally correct.  However, I believe
most iSCSI devices will be RAID or SAN-like boxes with JBODs.  The LUN and
block address of an iSCSI command are mapped into a cache memory location.
R2T is returned with a target task tag.  The incoming data messages will be
directed per target task tag to cache memory which later will be flushed to
JBODs.  In such context, you could say the LUN and iSCSI block address of an
iSCSI command as "advanced knowledge of segment content."  Of course, the
unsolicited write data do not apply.