linux-kernel - Re: [PATCH 10/13] iscsi-target: Add iSCSI Error Recovery Hierarchy support

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Date:	Thu, 28 Jul 2011 13:30:36 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Fubo Chen <fubo.chen@...il.com>
Cc:	target-devel <target-devel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>,
	Andy Grover <agrover@...hat.com>
Subject: Re: [PATCH 10/13] iscsi-target: Add iSCSI Error Recovery Hierarchy
	support

On Thu, 2011-07-28 at 13:42 +0200, Fubo Chen wrote:
> On Sat, Jul 23, 2011 at 10:45 AM, Nicholas A. Bellinger
> <nab@...ux-iscsi.org> wrote:
> > This patch adds support for RFC-3720 compatiable ErrorRecoveryLevel
> > support as defined in Section 6.1.5.  Error Recovery Hierarchy.
> >
> > This includes support for iSCSI session reinstatement, iSCSI within
> > command and within connection recovery, and explict/implict connection
> > recovery (CSM-E and CSM-I) from state machines in Section 7 of RFC-3720.
> >
> > These functions are called from iscsi_target.c to handle processing
> > based on the negotiated session-wide ErrorRecoveryLevel parameter.
> >
> > Signed-off-by: Nicholas A. Bellinger <nab@...ux-iscsi.org>
> 
> This is interesting. Is ERL2 similar to md ? If so, when should I use
> md and when ERL2 ?
> 

I think you mean dm-multipath and not md RAID here..

dm-multipath with TCM's ALUA multipath code provides a fabric
independent (iSCSI, FCoE, FC, SRP, etc) method of path failover across
multiple target ports for LUNs with a matching IEEE Extended Registered
WWN.

ERL=2 is a fabric dependent method of performing iSCSI connection
recovery on one or more failed TCP connections, where outstanding I/O
can be implictly retried and/or explictly migrated (TASK_REASSIGN) to an
active connection without having to restart the iSCSI I_T Nexus, or
notify the client side multipath layer that a I_T nexus has been lost.

Their use is not mutually exclusive, and can be used together to
complement one another.

--nab

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