Subject: Logical Block address in iSCSI CDB

From: "shesha bhushan" <[email-masked]>
Date: Tue, 03 Sep 2002 17:12:43 +0000

Hi,
  I established a full feature phase in ISCSI and mounted a disk from a 
remote machine. I copied a file from my local file system to the mounted 
disk. SCSI issues a series of Write commands that are encapsulated inside 
ISCSI PDUs.

My doubt is....  Do the logical block address contained in SCSI CDB inside 
ISCSI PDUs are actual address of the remote disk. Can we change that ????

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.

Any suggestions and indeas are highly appertiated.

Thanking You
Shesha
Arizona State University.

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From: Luben Tuikov <[email-masked]>
Date: Tue, 03 Sep 2002 16:35:28 -0400

> 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.