Greetings All!
Registered iSCSI logical units provided to the host OSes SCSI subsystem
speaking ERL=2 can preform session continuation within the context of
its own iSCSI Nexus. Traditional outernexus multipath software
(dm-multipath, MPIO, and others) require multiple iSCSI sessions to be
created to different ISIDs to same or different iSCSI TPG+LUN tuples in
order to perform their SCSI multipath recovery. The latter does this
and determines recovery logic using SCSI level SPC opcodes to test for
nexus establishment.
Connection recovery at the iSCSI level can make this happen very quickly
by detecting NOP response timeouts, link layer failures, TCP connection
resets and all types of ERL=1 events. So ERL=2 is benefical for all
types of storage devices (drives, tapes, CD/DVD roms) and allows less
reliable links (think wireless) to continue iSCSI IO operation in the
face of communication path failures and resets.
Thanks :-) !
Oh btw, core-iscsi is alive, it is currently in stable release and
accepting feature requests. Please check out the following wiki entry
for more information:
http://www.linux-iscsi.org/index.php/Core-iscsi_Interopt
--
Nicholas A. Bellinger <nickb@xxxxxxxx>
> > > On Sun, 2006-02-26 at 07:54 -0800, Rik Herrin wrote:
> > > > Thanks for your reply Ming. I understand that PyX
> > > > supports erl=2, but is it really important? If you
> > > > use HeaderDigest and BodyDigest (CRC32C) and since
> > > > iSCSI uses TCP, doesn't that take care of most errors?
> > > > I read the following: "However, just about every
> > > > vendor I questioned dismisses iSCSI error recovery
> > > > level 2 as unnecessary, at least for the time being,
> > > > because the protocol is already built on a robust
> > > > networking transport such as TCP, which already
> > > > guarantees data delivery and provides error checking.
> > > > [Sep. 2004]" "Nevertheless, many agree that iSCSI
> > > > error recovery level 2 could be useful in some cases.
> > > > For example, in case of errors, when the target device
> > > > is a tape, level 2 would allow the operation to
> > > > continue without having to restart."
> > > > (http://www.infoworld.com/article/04/09/03/36storinside_1.html
> > > > ) So isn't erl=2 only really useful for things such
> > > > as tapes? Wouldn't the initiator also have to support
> > > > it? How many initiators currently support erl=2? I
> > > > read that PyX used to have an initiator (core-scsi)
> > > > but that it's been discontinued. Thanks for your
> > > > input.
> > > >
> > > >
> > > > --- Ming Zhang <mingz@xxxxxxxxxxx> wrote:
> > > >
> > > > > as far as i know, there is no such comparison yet.
> > > > >
> > > > > feature wise, pyx support erl=2, mc/s. it run faster
> > > > > (not sure how much)
> > > > > on better HW like 10G.
> > > > >
> > > > > ming
> > > > >
> > > > >
> > > > > On Sat, 2006-02-25 at 06:09 -0800, Rik Herrin wrote:
> > > > > > Hi,
> > > > > > I was wondering if anyone had made a comparison
> > > > > > between the IET target in comparison with
> > > > > WinTarget
> > > > > > and PyX? I was thinking in terms of features,
> > > > > > performance, RFC compatibility, etc. Thanks for
> > > > > your help.
> > > > > >
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