Re: multipathd: sdc: readsector0 checker reports path is down

[Chandra Seetharaman <sekharan@us.ibm.com>]

On Thu, 2009-01-08 at 11:31 -0800, Ray Van Dolson wrote:
> I'm still getting the hang of iSCSI and multipath, so bear with me if
> this is a FAQ that I've missed...
> 
> I have a host attaching to an MD3000i via iSCSI/dm-multipath that is
> working but showing a lot of the following errors in syslog:
> 
>   multipathd: sdc: readsector0 checker reports path is down
you should be using the rdac path checker. In addition to that you
should be using rdac hardware handler and tpc priority checker.

If you have and entry for your MD3000i in /etc/multipath.conf, replace
it with this. If not add this
-------------------
devices {
        device {
                vendor                  "DELL"
                product                 "MD3000i"
                hardware_handler        "1 rdac"
                path_checker            rdac
                failback                immediate
                path_grouping_policy    group_by_prio
                no_path_retry           queue
                prio_callout            "/sbin/mpath_prio_tpc /dev/%n"
        }
}
---------------------

After this change you have to do:
- multipath -F
- service multipathd restart

Let me know how it goes.
> 
> My initial impression is that sdc is likely the "passive" path (for
> failover) whereas sdd is my active path:

yes.

> 
>   # multipath -ll
>   sdc: checker msg is "readsector0 checker reports path is down"
>   mpath2 (36001ec9000f338370000000000000000) dm-2 DELL,Universal Xport
>   [size=20M][features=0][hwhandler=0]
>   \_ round-robin 0 [prio=0][enabled]
>    \_ 4:0:0:31 sdf 8:80  [active][ready] 
>   mpath1 (36001ec9000f337dd0000000000000000) dm-1 DELL,Universal Xport
>   [size=20M][features=0][hwhandler=0]
>   \_ round-robin 0 [prio=0][enabled]
>    \_ 3:0:0:31 sde 8:64  [active][ready] 
>   mpath0 (36001ec9000f337dd0000065b491854a4) dm-0 DELL,MD3000i
>   [size=150G][features=0][hwhandler=1 rdac]
>   \_ round-robin 0 [prio=3][active]
>    \_ 3:0:0:0  sdd 8:48  [active][ready] 
>   \_ round-robin 0 [prio=0][enabled]
>    \_ 4:0:0:0  sdc 8:32  [failed][faulty]
> 
>   # iscsiadm -m discovery -t sendtargets -p 192.168.132.101:3260
>   0.0.0.0:3260,1 iqn.1984-05.com.dell:powervault.6001ec9000f337dd0000000048bdc862
>   0.0.0.0:3260,2 iqn.1984-05.com.dell:powervault.6001ec9000f337dd0000000048bdc862
>   192.168.132.101:3260,1 iqn.1984-05.com.dell:powervault.6001ec9000f337dd0000000048bdc862
>   192.168.132.102:3260,2 iqn.1984-05.com.dell:powervault.6001ec9000f337dd0000000048bdc862
> 
>   # iscsiadm -m session -P 1
>   Target: iqn.1984-05.com.dell:powervault.6001ec9000f337dd0000000048bdc862
>     Current Portal: 192.168.132.101:3260,1
>     Persistent Portal: 192.168.132.101:3260,1
>       **********
>       Interface:
>       **********
>       Iface Name: default
>       Iface Transport: tcp
>       Iface Initiatorname: iqn.1994-05.com.redhat:2738e0d3bd21
>       Iface IPaddress: 192.168.132.202
>       Iface HWaddress: default
>       Iface Netdev: default
>       SID: 1
>       iSCSI Connection State: LOGGED IN
>       iSCSI Session State: Unknown
>       Internal iscsid Session State: NO CHANGE
>     Current Portal: 192.168.132.102:3260,2
>     Persistent Portal: 192.168.132.102:3260,2
>       **********
>       Interface:
>       **********
>       Iface Name: default
>       Iface Transport: tcp
>       Iface Initiatorname: iqn.1994-05.com.redhat:2738e0d3bd21
>       Iface IPaddress: 192.168.132.202
>       Iface HWaddress: default
>       Iface Netdev: default
>       SID: 2
>       iSCSI Connection State: LOGGED IN
>       iSCSI Session State: Unknown
>       Internal iscsid Session State: NO CHANGE
> 
> sde and sdf are the silly 20MB partition that the MD3000 creates and
> I'm not using either.
> 
> My ultimate goal is to not have so many of the path is down errors
> showing up in my syslog file (hundreds and hundreds of them).  I'm not
> sure if their presence is normal (indicative of a passive path) or
> indicative of a problem.
> 
> Also, I'm not clear as to how I should identify which target
> corresponds with which drive (sdc or sdd).
> 
> Any thoughts?  I don't have direct access to the MD3000i
> unfortunately... this is from a CentOS 5.2 system btw.
> 
> Ray
> 
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