Logical unit groups and optional target reset

Tom Coughlan coughlan at missioncriticallinux.com
Thu Dec 21 06:54:49 PST 2000


* 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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