Logical unit groups and optional target reset

Andrew Hisgen Andrew.Hisgen at Eng.Sun.Com
Thu Dec 21 11:50:10 PST 2000


* From the T10 Reflector (t10 at t10.org), posted by:
* Andrew Hisgen <Andrew.Hisgen at eng.sun.com>
*
I share Tom C's concern.
--Andy Hisgen
Sun Microsystems

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 > Date: Thu, 21 Dec 2000 09:54:49 -0500
 > From: Tom Coughlan <coughlan at missioncriticallinux.com>
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 > To: "Elliott, Robert" <Robert.Elliott at COMPAQ.com>
 > CC: "'t10 at t10.org'" <t10 at t10.org>
 > Subject: Re: Logical unit groups and optional target reset
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 > * From the T10 Reflector (t10 at t10.org), posted by:
 > * Tom Coughlan <coughlan at missioncriticallinux.com>
 > *
 > Hi all,
 >
 > I agree with the goal of encouraging the implementation and use of
 > Logical Unit Reset. But, I'm not sure that dropping support for Target
 > Reset in future interconnects is a good idea.  Target Reset is the
 > medium weight hammer, between Logical Unit Reset, and resetting the
 > whole environment by, say, resetting the host bus adapter.
 >
 > I accept that there may be some target designs where resetting all the
 > logical units does all there is to do, and there is no point in
 > implementing a Target Reset.  But isn't it reasonable to expect that, in
 > some target designs, a Target Reset will clear a hung
 > something-or-other, that is not cleared by Logical Unit Resets?
 >
 > Shouldn't the decision to implement Target Reset be made based on the
 > design of the target, rather than the interconnect?
 >
 > --
 > Tom Coughlan
 > Mission Critical Linux
 > tel: 978-606-0262
 > coughlan at missioncriticallinux.com
 >
 >
 > "Elliott, Robert" wrote:
 > >
 > > * From the T10 Reflector (t10 at t10.org), posted by:
 > > * "Elliott, Robert" <Robert.Elliott at compaq.com>
 > > *
 > > John has posted these new proposals for me to 
http://www.t10.org.  Both are
 > > on the January CAP agenda.
 > >
 > > 01-015r0 Making Target Reset optional in SAM-2
 > >
 > > This would let new protocol standards like SRP and iSCSI drop support for
 > > Target Reset.  Target Reset is very disruptive in a SAN environment where
 > > different logical units on one target device are being used by different
 > > initiators.  Logical Unit Reset is a better tool.
 > >
 > > SRP and iSCSI drivers can map legacy Target Reset requests into 
Logical Unit
 > > Resets for every logical unit the initiator is using.  This avoids
 > > disrupting other initiators using other logical units.  Its absence from
 > > future standards may help wean software from issuing Target Resets.
 > >
 > > 01-004r0 Logical unit groups
 > >
 > > This works in conjunction with 00-232r3 Asymmetric SCSI behavior (Ken 
Moe),
 > > which defines "target port groups."  A logical unit group defines a set of
 > > logical units that always maintain the same target port group states.
 > >
 > > ---
 > > PC: Robert.Elliott at compaq.com
 > > UNIX: relliott at unixmail.compaq.com
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