Help with multipath failover

Brian O'Mahony brian.omahony at curamsoftware.com
Tue Apr 6 07:51:31 CDT 2010


Sorry for the delay in responding to this. I was away at the end of last week.

Anyways, to test I was running a ping from one terminal and then using the other terminal to run multipath -ll, and as far as I can see the actual multipathing is fine. However the machine isn't in the office and there is no-one on site till the morning.

What method would you suggest to measure if the I/O is interrupted? I would have thought if the ping was unsuccessful, then so to would be read/writes?

I also have two other quick questions:

1. Where do you go about deleting multipath configuration? When I use multipath -F it tells me the map is in use, so I stopped the service and logged out of the node, but the error stays the same.

2. Is there any tools you would recommend for monitoring read/write access to the SAN once it is in production? I just want to be able to monitor, preferably in real time, the read/write speeds, and whether there is bottlenecks - eg with the network to the SAN.

Thanks for all the help
B

-----Original Message-----
From: Shyam_Iyer at Dell.com [mailto:Shyam_Iyer at Dell.com] 
Sent: Wednesday, March 31, 2010 7:51 PM
To: Brian O'Mahony; criley at erad.com; linux-poweredge at lists.us.dell.com
Subject: RE: Help with multipath failover



Well you are testing link failover and not I/O failover then .. (:


I would ideally try to do I/O through one path yank out the cable and watch the I/O failover to the other path...
That is probably what you want to ensure if you want to use dm-multipath..

Also, make sure you change the configuration for failback from "immediate" to "queue" so that you won't see immediate I/O failures and see the I/O safely failover to the other path.

Thanks,
Shyam Iyer
Linux Engineering.

-----Original Message-----
From: linux-poweredge-bounces at dell.com on behalf of Brian O'Mahony
Sent: Wed 3/31/2010 2:02 PM
To: 'criley at erad.com'; linux-poweredge-Lists
Subject: Re: Help with multipath failover
 
Ping to san ip and yanking a cable....
------------------------
Sent from my BlackBerry Wireless Handheld


----- Original Message -----
From: Charles Riley <criley at erad.com>
To: Brian O'Mahony
Sent: Wed Mar 31 18:34:12 2010
Subject: Re: Help with multipath failover

How are you determining that it doesn't fail over?

Charles Riley
eRAD, Inc.


----- "Brian O'Mahony" <brian.omahony at curamsoftware.com> wrote:

> Im connecting a PE2850 to a Equalogic SAN, using multipath. I have a
> PCI NIC with one connection to the SAN and one from the onboard
> controller too. The SAN is ona different network, and is at IP
> 10.10.20.10.
> 
> 
> 
> Here is the output from the multipath -ll
> 
> [root at ccvobtest2850 ~]# multipath -ll
> 
> DubSanGrp01VolCC (36090a048d03f308d51b1f47c000030a6) dm-18
> EQLOGIC,100E-00
> 
> [size=500G][features=1 queue_if_no_path][hwhandler=0][rw]
> 
> \_ round-robin 0 [prio=1][enabled]
> 
> \_ 3:0:0:0 sdc 8:32 [active][ready]
> 
> \_ round-robin 0 [prio=1][enabled]
> 
> \_ 4:0:0:0 sdd 8:48 [active][ready]
> 
> 
> 
> 
> 
> 
> 
> And here is the multipath.conf:
> 
> [root at ccvobtest2850 ~]# cat /etc/multipath.conf
> 
> ## Use user friendly names, instead of using WWIDs as names.
> 
> defaults {
> 
> user_friendly_names yes
> 
> }
> 
> blacklist {
> 
> # wwid 26353900f02796769
> 
> # devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
> 
> # devnode "^hd[a-z]"
> 
> # devnode "^sd[a-b]"
> 
> }
> 
> multipaths {
> 
> multipath {
> 
> wwid 36090a048d03f308d51b1f47c000030a6
> 
> alias DubSanGrp01VolCC
> 
> }
> 
> }
> 
> devices {
> 
> device {
> 
> vendor "EQLOGIC"
> 
> product "100E-00"
> 
> path_grouping_policy failover
> 
> getuid_callout "/sbin/scsi_id -g -u -s /block/%n"
> 
> features "1 queue_if_no_path"
> 
> path_checker readsector0
> 
> failback immediate
> 
> path_selector "round-robin 0"
> 
> rr_min_io 10
> 
> rr_weight priorities
> 
> }
> 
> }
> 
> 
> 
> 
> 
> However when I unplug the cable to eth1, it doesn't failover. I am
> testing with a ping to the SAN at 10.10.20.10. As Im pretty new to all
> this, was wondering if anyone has any pointers on where I am going
> wrong.
> 
> 
> 
> Thanks
> 
> Brian
> 
> 
> 
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