Logical unit groups and optional target reset

Charles Monia cmonia at NishanSystems.com
Thu Dec 21 10:49:27 PST 2000


* From the T10 Reflector (t10 at t10.org), posted by:
* Charles Monia <cmonia at NishanSystems.com>
*
Hi Folks:

There's a difference between 'must support' and 'must allow every initiator
to use'.  In an open networked environment, it may be a good idea to limit
access to certain classes of operations to 'privileged initiators'.

I believe we need to reexamine all SCSI operations in that light.  For
example, do we want to allow any initiator to reset a shared LU or have
unrestricted access to its mode pages?

Charles
> -----Original Message-----
> From: Tom Coughlan [mailto:coughlan at missioncriticallinux.com]
> Sent: Thursday, December 21, 2000 6:55 AM
> To: Elliott, Robert
> Cc: 't10 at t10.org'
> Subject: Re: Logical unit groups and optional target reset
> 
> 
> * 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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