[stgt] [PATCH] release backing store when offline

FUJITA Tomonori fujita.tomonori at lab.ntt.co.jp
Sat Jul 16 11:27:37 CEST 2011

On Thu, 14 Jul 2011 08:07:23 -0500
"James R. Leu" <jleu at inoc.com> wrote:

> We are building a geographically redundant SAN that will allow 
> each LUN to be active on one node and passive on the other node
> independent of the other LUNs.  To accomplish this we we
> need to be able to mark a LUN as offline and have it release the
> reference to the underlying block device so we can make it passive.

Why can't the passive target simply add a LUN instead of keeping it as
offline? Then when the active target fails, the passive target can add
the LUN?

> DRBD is doing the block level replication and asserts the notion
> of active/passive.  It will not allow a block device to transition
> to passive if anything is holding a reference to it.
> The iSCSI clients of the SAN are geographically redundant as well.
> The resources on those clients need to be able to migrate between the
> datacenters independent of each other.  To accomplish this it is
> highly desirable to keep the TGTD configuration nearly identical
> on the nodes of the SAN so that the redundant iSCSI clients see
> the same LUNs no matter if their local resources are active or passive.
> If my patch does not appear to be anything you want in the
> main distribution could you at least look it over to see if I am
> overlooking anything?

I don't think that it's a good idea to close a LUN when making it
offline. Making a LUN offline means that it reuses it later. There is
no point to close (release) it.
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