[stgt] [PATCH] iscsi: target redirect support

[Chandra Seetharaman]

On Wed, 2010-06-16 at 12:36 +0900, FUJITA Tomonori wrote:
> On Tue, 15 Jun 2010 12:13:32 -0700
> Chandra Seetharaman <sekharan at us.ibm.com> wrote:
> 
> > > > In effect, (1) I think we need to be able to mark the redirector tgtd as
> > > > such (with an option in the command line or such),
> > > 
> > > I'm not sure why we need this since sounds like you can avoid the
> > > issue with a proper targets.conf.
> > 
> > Looks like using the targets.conf file itself avoids the problem...
> > but...
> > 
> > having a separate "designated" redirector would allow
> >  - to have single node to which the initiators always connect
> >  - to run the "redirector" in a node which doesn't actually have the 
> >    backing store
> 
> You can do it now. You can configure a target to be redirected
> somewhere without adding luns.

By virtue of the backing store not being there... I see..
> 
> >  - avoid unnecessary creation of the threads for the luns (with 1 lun in
> >    both of my targets, i see 10 more threads og tgtd).
> 
> What version of tgt do you use?

1.0.3, I guess... Will try the latest.

> 
> As I wrote above, you can configure a target having only lun0 to be
> redirected. We create only one pthread per target. We don't create any
> threads for lun0.
> 
> 
> >  - Have the redirector definition in targets.conf itself (which would
> >    mostly be the case ?!)
> 
> That's a different issue. We can configure the redirect via tgtadm
> now. All you need to do is modifying tgt-admin to support it. No need
> to modify tgtd or tgtadm.

If/when we add redirector support to tgt-admin, how the two tgtds
(redirector tgtd and serving tgtd) know to treat the redirector
instructions differently ? i.e redirector tgtd should use the
information and "serving" tgtd should not. Basically the tgtd should be
knowing if it is a "redirecting" tgtd or "serving" tgtd.

Details:
targets.conf file 
---------------------
<target iqn.2010-03.com.cluster1:01>
        <backing-store /gpfs/file1>
		vendor_id cluster1
		product_id target1
		scsi_id cluster1_target1_lun1
                lun 1
        </backing-store>
	initiator-address 10.0.0.1
	redirect-address  10.0.1.51
        redirect-port     860
        redirect-reason   Temporary
</target>
--------------------

And if i were to use tgt-admin to control the tgtds with the same
targets.conf file, how will the tgtd ot tgt-admin know which tgtd to
sent the redirect stuff and which one to not to.

Hence, I was requesting a way to mark a tgtd as a redirector tgtd.

Thinking more on this issue, I came up with another issue/solution. Will
start a different thread (for easier handling :).
> 
> 
> > What do you think ?
> > > 
> > > btw, I think that we need to modify the redirect configuration on the
> > > fly so I avoided the command line.
> > 
> > I see that as a plus, but in a deployed environment won't the user want
> > to have these in a static place, like targets.conf ?
> 
> See above. That's a different issue. Please send a patch for tgt-admin
> to support to configure redirection. I'm happy to apply it.
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