[dm-devel] FW: How to avoid lots of read ios to passive paths of active-pass ive storage devices?

[goggin, edward]

Reposting since it didn't get much response initially and the issue came up
again
in yesterday's multipath conference call.

> ______________________________________________ 
> From: 	goggin, edward  
> Sent:	Friday, July 08, 2005 12:21 AM
> To:	'dm-devel at redhat.com'
> Subject:	How to avoid lots of read ios to passive paths of
> active-passive storage devices?
> 
> How sould device scanning utilities like blkid, pvscan,
> vgscan, and lvscan (others?) be made to avoid issuing
> a significant number of read ios to passive paths of
> active-passive storage devices?
> 
> Possibly they could be changed to use device specific
> command interfaces like SCSI pass through ioctls to
> read the native device paths in order to avoid sending
> lots of ios down the passive paths to active-passive
> storage devices?
> 
> This way they could parse the sense key, ASC, and ASCQ
> returned via the SG_IO interface, see values like
> "Not Ready, Manual Intervention Required" and avoid
> sending subsequent reads to the same path.
> 
> Or should they be changed to scan the multipath devices
> if they exist instead of the path specific devices?
> 
> While this isn't an issue now, it could become one later
> when/if linux hosts are configured with hundreds/thousands
> of passive paths.
>