[dm-devel] Re: fastfail operation and retries

[Lars Marowsky-Bree]

On 2005-04-21T23:33:57, Andreas Herrmann <aherrman at de.ibm.com> wrote:

> Well, there are various situations when all paths to the ESS are
> "temporarily unavailable". In some cases TASK_SET_FULL/BUSY is
> reported as it should be.

Not sure whether this sense data is decoded and handled correctly in
dm-mpath yet. I don't have detailed specs, nor a feature request to
allocate time to work on making sure it really does. I recommend that
someone at IBM takes the real specs for the ESS and makes sure that it
all works, by a combination of the right defaults in the multipath-tools
hwtable and, if need be, a dm-ess plugin to handle this.

This would be much appreciated.

> underruns or exchange sequences are aborted and finally it might be
> that requests just time out. BTW, it is not only ESS where I have seen
> such (broken) behaviour.

Well, what can I say. Broken behaviour needs to be documented and worked
around, but obviously only as far as that is possible.

> > It is possible that to fully support them a dm mpath hardware handler
> > (like for the EMC CX family) might be required, too.
> For the time being I hope "queue_if_no_path" feature is sufficient
> to succesfully pass our tests ;-)

If it is sufficient, you might at least wish to update the
multipath-tools hwtable entry so that it is automagically set for your
arrays.


Sincerely,
    Lars Marowsky-Brée <lmb at suse.de>

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