Re: Several Questions.

[julian_satran@il.ibm.com]

Kim,

SCSI has a bit more than the CDB. It has a "task-tag" that enables several
commands
to be queued by a device, a selector for a unit, specification of the
transfer length, an address where to place data, a response, a target
address.

All of them are specified in SAM-2.

Their mapping is infrastructure specific.

As for NFS versus SCSI - NFS is a file oriented protocol while SCSI is (for
a while) a
block transfer protocol.

They are used by different application classes.

It is possible that they will "converge" into a common successor  but it
will take a while until this will happen if it will happen.

Julo

Kim Tae Hyung <kotaeji@pilots.postech.ac.kr> on 03/08/2000 18:18:12

Please respond to kotaeji@postech.ac.kr

To:   ips@ece.cmu.edu
cc:    (bcc: Julian Satran/Haifa/IBM)
Subject:  Several Questions.





Hi, all. I am a graduate student who is very interested in
iSCSI. Although I feel very difficult, I am trying to follow up the
articles in this mailing list.

Reading the articles in this mailing list nowadays, I cannot fully
understand every new issue.

By the way, with my amateur's eyes, some very basic questions have
made me write this article.

The first question is about the SCSI protocol itself. iSCSI is just a
mapping the SCSI protocol to TCP. But looking in details, I think that
it is just the mapping of CDB. After removing the unnecessary parts of
SCSI protocol due to the change of underlying physical media from bus
to network, I think just CDBs remain, eventually. Then how can we map
the operation sequence of SCSI protocol to that of iSCSI ? I wonder
whether we can call this just mapping of CDB to SCSI protocol.
I think CDB is not the everything of SCSI.

The second question is the distinct differences between NFS and
iSCSI. According to "draft-von-ipsissues-01.txt" file, there are the
following paragraph.

4.2.4 NFS
"NFS is the current solution for accessing storage over the
network. Its strengths are ease-of-use, file sharing, and
security. The general assumption is that a block storage protocol
should outperform NFS in some applications, but that assumption needs
to be tested. Also, some applications (e.g. tape library) could
benefit from a block storage protocol.  In order for a block-based
solution to be accepted, clear benefits over NFS (e.g. performance,
direct access) must be proven, Even then, NFS would still be the
solution of choice for those requiring ease-of-use and file sharing."

6. Conclusion

   - Any block storage protocol must show clear differentiation from
NFS.



I want to hear many opinions about the distinct differences between
the file protocol such as NFS and iSCSI.

Thanks in advance.