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Re: [dm-devel] Can DM-Multipath work on non-SCSI block device



On 03/14/2013 11:41 AM, Bryn M. Reeves wrote:
On 03/14/2013 09:29 AM, Hannes Reinecke wrote:
On 03/14/2013 08:58 AM, Ahmed Al-Mehdi wrote:
Hello,

I read the documentation on the dm-multipath home page:
htttp://christophe.varoqui.free.fr/refbook.html
<http://christophe.varoqui.free.fr/refbook.html> , that describes
how the userspace multipath tool detects and maps (scsi) devices.
However, would like to confirm, does the dm-multipath utilty only
work with SCSI devices.  Is there any option to make it (or fake it)
to work with non-SCSI  block device.

If you can figure out a way on how to get a unique _disk_ id without
SCSI, sure.

E.g. cciss devices are supported using the cciss_id program - that's
a good example of a very "non-scsi" device type working with multipath.

As well as the WWID problem you'll need to come up with some scheme
for faking unique HCIL values for the devices since multipath
userspace cares about that. The cciss approach is to force lun and
channel to '0' for all devices and to use the CCISS controller (cN)
and disk (dN) values for the host and id (aka target) values.

See the functions in discovery.c with a cciss_ prefix for more
examples.

Or the dasd variant of those.

However, the HCIL variable is mostly cosmetic.
The disk id is the true issue; without it you cannot do multipathing.

Cheers,

Hannes
--
Dr. Hannes Reinecke		      zSeries & Storage
hare suse de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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