[dm-devel] [multipath] meaning of "no_path_retry nn"

[Moger, Babu]

This is how the time is calculated. 
Total queing time =  nn* polling_interval.

For example 
	polling_interval        10
	no_path_retry 		5

This will queue-up the i/os for 50 seconds. You should see i/o error after 50 seconds in case of all path failure.

However, this may not work in all the distros. We have seen problems with this feature. Looks like upstream tool has fixed this problem.
 
Thanks
Babu Moger 

> -----Original Message-----
> From: dm-devel-bounces at redhat.com [mailto:dm-devel-bounces at redhat.com]
> On Behalf Of Diedrich Ehlerding
> Sent: Friday, August 28, 2009 8:16 AM
> To: dm-devel at redhat.com
> Subject: [dm-devel] [multipath] meaning of "no_path_retry nn"
> 
> I would appreciate an explanation of "no_path_retry nn" parameter in
> multipath.conf. Probably I misunderstood it as a number of seconds.
> 
> I am setting up  a software mirror (mdadm) on top of an EMC Clariion
> configuration for desaster protection. The Clariions are recognized by
> multipath properly; it seems to be set up with "no_path_retry 60"
> (according to multipath -t). I had no further settings in
> multipath.conf; this seems to be hardcoded into multipath.
> 
> However, If I disconnect one Clariion, th mirror doesnt break -
> multipath detects that all paths are failed and tells me that it will
> now wait for 60 retries. These 60 retries seem to last very long;
> atfter 5 minutes, it didnt complete.
> 
> Evertyhing works fine if I set up a multipath.conf containing the
> Clariion settings from multipath -t and modify them to
> "no_path_retry fail" and "features 0 fail_if_no_path".  But even if I
> just reduce the default settings to no_path_retry 2 the mirror doesnt
> break - the IOs seem to hang indefinitely (well, I lost patience after
> ~5 minutes).
> 
> Probably I misunderstood "no_path_retry 60" - does that mean seconds,
> or minutes, or what else? Is anything except "fail" a useful setting in
> mirrored configurations?
> 
> system is a Suse  with multipath-tools-0.4.7-34.43
> 
> Thanks
> Diedrich
> --
> Diedrich Ehlerding, Fujitsu Technology Solutions GmbH, R GE TIS N IC2
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