IO error issues with MD3000i on Linux

[Shyam_Iyer at Dell.com]

> -----Original Message-----
> From: linux-poweredge-bounces at lists.us.dell.com [mailto:linux-
> poweredge-bounces at lists.us.dell.com] On Behalf Of Scott Ehrlich
> Sent: Friday, June 19, 2009 6:55 AM
> To: linux-poweredge-Lists
> Subject: Re: IO error issues with MD3000i on Linux
> 
> Here is a basic question -
> 
> dmesg shows many errors from the md3000i.   Newer kernels treat the
> "errors" more appropriately.
> 

True. Newer kernels like 2.6.27~ and above have a scsi device handler
module (scsi_dh_rdac) which can handle active/active, active/passive
paths effectively.


> My question is - are the errors really bad errors?   Is the hardware,
> or is the data, really in trouble?  Or, are the logged errors simply
> benign software reports that the kernel and drivers don't know any
> better how to deal with the responses from the md3000i, but the data
> and hardware are all fine?
> 

Currently, stock rhel-5.3 has the module backported but without the
support for the MD3000i device. Patches + kernel fix available in
bugzilla https://bugzilla.redhat.com/show_bug.cgi?id=487293 for quick
peak.

The default path_selector "readsector0" can't make effective decisions
on active and passive paths.

The right way to do this is possibly load the scsi_dh_rdac module(with
support for MD3000i) and use the following multipath.conf -

blacklist {
	device {
			vendor                  "DELL"
			product                 "Universal Xport"
		}
	}
devices {
	device {
		vendor			"DELL"
		product 			"MD3000i"
		getuid_callout		"/sbin/scsi_id -g -u -d
/block/%n"
		getuid_callout		"/lib/udev/scsi_id -g -u -d
/block/%n"
		prio_callout		"/sbin/mpath_prio_rdac /dev/%n"
		prio				rdac
		features			"0"
		hardware_handler		"1 rdac"
		path_grouping_policy	"group_by_prio"
		failback			"immediate"
		path_checker		"rdac"
		no_path_retry		queue
		queue_if_no_path     	1
	}
}

And finally restart the multipathd. 

Please check your paths using "multipath -ll"

-Shyam Iyer