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RE: iSCSI question
Shahram,
1)
Connection reassignment requires more than PDU retransmission to
handle corner cases
2) Error recovery level 1&2 requires more buffering which
takes space and lowers performance. If
you support error recovery level 1 you might as well support
level 2.
Amir
Pat,
Thanks. I understand your point. Although terminating
a session may be easy, but, starting a new session requires new login,
parameter exchange, new connections establishment, authentication, etc. So I
wonder how is this any simpler than a simple PDU
retransmit?
Yours,
-Shahram
Shahram,
Wen you start a
new session, you don't recover any PDUs. All the iSCSI state died with the
old session. iSCSI doesn't know the new session had any relationship to the
old session.
As Julian said,
recovery at that point is up to the SCSI layer above iSCSI. It is up to SCSI
to retry any commands that it wants to retry. When SCSI retries a command,
iSCSI doesn't know it is a retry. To the iSCSI layer it is just like any
other SCSI command it receives.
Pat
Julian,
To
start a new session you need to start new connections and you need to
support
the PDU recovery. So how is that a subset of PDU
and connection recovery?
-Shahram
(I will explain the detailed clarity issues in
another email)
Session
recovery is in fact leaving all recovery to SCSI - it drops everything and
creates a new session.
As for you
comment on the clarity of chapter 5 at this stage it makes sense to be
either specific
or keep this type
of comment out of this context.
Julo
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| Shahram Davari
<Shahram_Davari@pmc-sierra.com>
08/07/2002 06:09 PM
|
To: Julian Satran/Haifa/IBM@IBMIL
cc:
ips@ece.cmu.edu,
owner-ips@ece.cmu.edu
Subject: RE: iSCSI
question
|
Julian,
Thanks. I have
read that section but it is not very clear.
I also agree that Connection recovery requires
everything in command recovery.
But what about session recovery? isn't it a superset of both
connection and command recovery?
Yours,
-Shahram
-----Original Message-----
From: Julian
Satran [mailto:Julian_Satran@il.ibm.com]
Sent: Wednesday, August
07, 2002 11:03 AM
To: Shahram Davari
Cc:
ips@ece.cmu.edu; owner-ips@ece.cmu.edu
Subject: Re: iSCSI
question
Sharam,
You may want to go over the
recovery chapter.
It has detailed answers to all your
questions.
The superset/subset is based on functions you
need for the next level.
Session recovery drops real
recovery to SCSI.
Command recovery recovers from individual
command errors without
changing connection and the highest enable you
to switch to a new connection and
continue commands
there.
2 requires everything in 1.
Julo
|
| Shahram Davari
<Shahram_Davari@pmc-sierra.com>
Sent by: owner-ips@ece.cmu.edu
08/07/2002 05:17 PM
|
To: ips@ece.cmu.edu
cc:
Subject:
iSCSI question
|
Hi,
I have a question regarding the hierarchy of error
recovery.
Section 6.13 mentions the hierarchy as:
2: Connection
recovery
1: Digest failure recovery
0: Session recovery
And
it states that the higher levels are a superset of the
lower levels and
that the level of complexity increases from 0->1->2.
Couple
of questions:
1) How is digest failure recovery done? by
retransmission of PDUs?
2) Why is the connection recovery a superset of
session recovery
and more complex?
3) It seems to me the order
should be:
2: Session recovery
1: Connection recovery
0:
Digest failure recovery
I appreciate any
insight.
Thanks,
-Shahram
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Last updated: Thu Aug 08 17:18:58 2002
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