On Mon, Nov 5, 2018 at 3:10 AM Ulrich Windl <
ulrich.wi...@rz.uni-regensburg.de> wrote:

> Hi!
>
> I wonder: On Fibre-Channel (FC) SAN stroage systems, some systems indicate
> when there are new LUNs available, while others do not. Linux clients
> sometimes understand what the storage system is telling them, sometimes
> not. So usually one has to rescan the scsi bus to find new (or obsolete)
> LUNs.
> Does the SCSI protocol have provisions to indicate a new target is
> available? Maybe it depends on the details: I'd guess a device that is in
> the state of becoming ready would be detected, but would have a state like
> "target is becoming ready" (which could be polled using TUR, I guess).
> If the whole storage system is down, the situation is different, but in
> the FC case a new target would be still signalled on the FC bus at least
> (via LIP (loop Initialization Primitive) I think)...
>
> Could such events trigger an iSCSI login?
>
> Regards,
> Ulrich
>
>
FC: has RSCNs. Most enterprise arrays send them and Ini will do the
appropriate thing.
FC: LIP. This is on the backend enclosure on the storage/target systems and
isn't related to the Initiator. Its upto the target how it wants to send
the events. LIPs are(or atleast were) common and targets handle them
internally else Ini will get overwhelmed with something it doesn't really
care about.

iSCSI: Look at iscsid.conf: node.session.scan=auto

ZFS targets for example do send AENs to the Ini upon a LUN add/remove. But
on a large site(1K+ LUNs on an ini), we were running into issues(no fault
of the target) on the Initiator side...race conditions: if you have
parallel removals (which will happen on a large cloud site) then you may
run into some discovery issues.

And so we took care of it in the control plane as opposed to changing the
kernel. And then later on, open-stack ran into something similar and a fix
was added to disable or enable auto-scan.


Chetan

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