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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SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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