Re: Status of SCSI referrals support in dm-multipath

[Hannes Reinecke <hare@suse.de>]

On 06/01/2014 10:46 PM, Sebastian Herbszt wrote:
> Hello,
>
> I am trying to find out the status of SCSI referrals support in dm-multipath.
> SCSI referrals support was a topic at LSF [1] but I wasn't able to find any
> information. Back in 2010 Hannes suggested the use of multiple entries in a
> multipath table [2] but this doesn't seem to work (anymore):
>
> [ 7750.354190] device-mapper: table: Request-based dm doesn't support multiple targets yet
>
> Is there any SCSI referrals support yet?
>
> [1] http://marc.info/?l=linux-scsi&m=129553880112460&w=2
> [2] http://www.redhat.com/archives/dm-devel/2010-June/msg00155.html
>
Not as of now. I've managed to push referrals support into 
target_core, so you now can set up a backend which supports referrals.

And for the multiple entries I've though to use a linear target on 
top of the multipath target.
The linear target would just split up the device in chunks, 
according to the referrals layout.
And then you would have several multipath devices (all referring to 
the same disk), one for each supported referrals ALUA configuration.
The linear target would then map each chunk to the correct multipath 
device.

It'll be a beast for failover, but should be possible.
And maybe it's better to use dm-switch here; the number or referrals 
might overflow dm-linear ...

Cheers,

Hannes

-- 
Dr. Hannes Reinecke		      zSeries & Storage
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