Re: Logical Block address in iSCSI CDB

[Luben Tuikov <luben@splentec.com>]

shesha bhushan wrote:
> 
> What I am trying to do is,.......
> 
>   If SCSI sends only 2 block or 3 blocks, wait and collect data upto 16
> blocks (Usual max PDU of ISCSI) and send them over the network so that it
> will reduce the header over-head.
> 

An iSCSI implementations should support clustering of requests.
Clustering of requests goes hand in hand with the elevator algorithm.
(<<long lecture on those two concepts here to be read in your alma
mater's library>>)

The Linux block layer and SCSI core, support clustering and the IOL/UNH
implementation (which is the one you are using) should _enable_ it (please
don't tell me if it does/doesn't -- I don't care).

Please note that you are saying ``... wait and collect ...'', at which
point you've overruled an implementation of being fast.

Please further note, that as an interconnect/transport, iSCSI
has NOTHING to do with any of this.

Please also don't assume the size of a ``block'' and the size
of the iSCSI PDU.

A self-respecting OS should've optimized the requests before
submitting them down to the interconnect driver (FC/SPI/iSCSI/etc).
Linux would do that for you if you've enabled clustering.
Thus if speed is what you're after, I'd suggest you use
a commercial iSCSI solution.

-- 
Luben

P.S. Please just let us know what you are _actually_ trying to do,
rather than putting ellipsis at the end of your sentence.
I certainly hope you are not trying to do your assignment,
else we should NOT be replying to you.

We could give you a lot more and invaluable help rather than
you asking details and trying to put their answers together.