Re: Can DM-Multipath work on non-SCSI block device

[Hannes Reinecke <hare@suse.de>]

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
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