[stgt] Support for persistent reservations

Mike Anderson andmike at linux.vnet.ibm.com
Fri Oct 1 18:56:43 CEST 2010

Lars Kellogg-Stedman <lars at oddbit.com> wrote:
> Hello all,
> The fence_scsi method provided with RedHat's cman package uses SCSI
> persistent reservations as an i/o fencing mechanism.  I've tried using
> this against an iSCSI target served by tgtd without much luck.
> The tool is able to successfully create a reservation by running:
>   sg_persist -n -d <device> -o -R -K <key> -T 5
> fence_scsi uses --preempt-abort to fence another node (prevent it from
> accessing a device) by running:
>   sg_persist -n -d <device> -o -A -K <local key> -S <other key> -T 5
> This results in the following error from sg_persist:
>   PR out: bad field in cdb including unsupported service action
> I'm using the version of scsi-target-utils distributed with Fedora 13
> (scsi-target-utils-1.0.1-4.fc13.x86_64).  Has anyone else run into
> these problems?  Is this expected to work?
> The tgt configuration looks like this:
>   default-driver iscsi
>   <target iqn.2001-04.com.obliquity-tgt-1>
> 	backing-store /var/lib/libvirt/images/shared.img
>   </target>
> I see the same error message with tgtd 1.0.9.  Additionally, both
> versions appear to freeze up completely if I try to use --preempt
> instead of --preempt-abort.

The PR_OUT_PREEMPT_AND_ABORT service action is currently not supported.
You may have already seen this by the commented out service action in

I am seeing the freeze also. We are in a endless goto loop in
spc_pr_preempt based on a non-zero service action key.

Working on a patch for the --preempt case now by verifying the code vs.
the preempt flow chart in the spc specification. I assume you are more
interested in the support for --preempt-abort. I will look at this next
unless others are already working on it.

Michael Anderson
andmike at linux.vnet.ibm.com
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