On Nov 4, 2014, at 11:22 PM, shivraj dongawe <[email protected]> wrote:
> Dear Ulrich,
>
> Is there any concrete implementation available for scatter/gather
> mechanism ?
> If available, how could we use with iSCSI initiator and target
> combination?
>
> Thanks and Regards
>
> Shivraj K Dongawe
You may be talking about different things.
Scatter-gather is an OS service. It takes a single I/O request (single SCSI
operation) but splits the buffer up into several parts. From the SCSI point of
view you still see a single request: it addresses a single starting LBA and
length.
I think Shrivraj was talking about a different notion that has been discussed a
bit: a single SCSI command that combines several starting LBA/length pairs. I
don’t see any point in that; you can achieve the same result simply by queueing
up multiple operations. There might be a slight difference in network and I/O
system overhead, but I can’t see a good reason to expect it to be significant.
And the complexity of such a “multiple I/O operation” command would be
substantial.
In any case, if such a thing were done it would be in SCSI, not iSCSI; it would
be transparent to iSCSI.
paul
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