Subject: Re: [Ips] Reservations, multiple sessions and ISID usage

From: [email-masked]
Date: Sat, 13 Mar 2004 10:35:50 -0500

>How do these rules affect the implementation of SCSI reserve and release
in a load balancing environment where there are >multiple sessions to a
target ? What criteria does the target use to determine that all of the
sessions are from the same initiator >for the purposes of reserve so as to
allow load balancing to occur over the multiple sessions ?

I think that a the target should not have to detect multiple session
load balancing OS's.  I think that this view is in line with the iSCSI
specification (references cited below).

I do have some related questions and comments
1. Do other SCSI transport protocol targets detect load balancing OS's
using multiple initiators?
2. If a target does not detect load balancing then the reserve/release
would be a bottleneck (that resource path would be locked), but multiple
connection sessions solves this problem and is well defined.  Other
that lack of target support, why can't multiple connection sessions
be used instead?

>From Sec. 9.1.2
 The designers of the iSCSI protocol envisioned there being one iSCSI
   Initiator Node Name per operating system image on a machine. This
   enables SAN resource configuration and authentication schemes based
   on a system's identity. It supports the notion that it should be
   possible to assign access to storage resources based on "initiator
   device" identity.
Sec. 2.1
   - Session: The group of TCP connections that link an initiator with
   a target form a session (loosely equivalent to a SCSI I-T nexus).
   TCP connections can be added and removed from a session. Across all
   connections within a session, an initiator sees one and the same
   target.
>From Sec. 9. (my favorite)
   The guiding assumption made throughout the design of this protocol
   is that targets are resource constrained relative to initiators.

I would appreciate any comments or corrections.

Aaron

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From: Andre Hedrick <[email-masked]>
Date: Sat, 13 Mar 2004 19:06:44 -0800 (PST)

Aaron,

The way to load balance effectively is to execute dispatch without the use
of 802.3ad.  If the balance is dependent on a network stack and 802.3ad
dependency, one generates the single point of failure on the subnet.

Each session should have describe a base queue depth after FFP.

Doing dynamic load balance was found to be rude to sleeping initiators
logged in currently.  If a new session(different initiator) completes
discovery/login to FFP and there is a resource limitation because of
existing allocations, one can not collapse the two windows on a sleeping
initiator.  Thus to free resources, one has to rudely kick an initiator
off and force it to perform session re-instatement.

One could grab another chunk of host-memory, but then face the race
condition of allocation failures.

Just a comment.

Cheers,

Andre