[LSF/MM ATTEND][LSF/MM TOPIC] Multipath redesign

[Hannes Reinecke <hare@suse.de>]

Hi all,

I'd like to attend LSF/MM and would like to present my ideas for a 
multipath redesign.

The overall idea is to break up the centralized multipath handling 
in device-mapper (and multipath-tools) and delegate to the 
appropriate sub-systems.

Individually the plan is:
a) use the 'wwid' sysfs attribute to detect multipath devices;
    this removes the need of the current 'path_id' functionality
    in multipath-tools
b) leverage topology information from scsi_dh_alua (which we will
    have once my ALUA handler update is in) to detect the multipath
    topology. This removes the need of a 'prio' infrastructure
    in multipath-tools
c) implement block or scsi events whenever a remote port becomes
    unavailable. This removes the need of the 'path_checker'
    functionality in multipath-tools.
d) leverage these events to handle path-up/path-down events
    in-kernel
e) move the I/O redirection logic out of device-mapper proper
    and use blk-mq to redirect I/O. This is still a bit of
    hand-waving, and definitely would need discussion to figure
    out if and how it can be achieved.
    This is basically the same topic Mike Snitzer proposed, but
    coming from a different angle.

But in the end we should be able to do strip down the current 
(rather complex) multipath-tools to just handle topology changes; 
everything else will be done internally.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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