[dm-devel] Failing on NIC removal

[Mike Christie]

Mike Anderson wrote:
> cc'ing open-iscsi
> 
> Scott Moseman <scmoseman at gmail.com> wrote:
>> So I finally got my multipath running through both the NIC and HBA
>> interfaces, but I'm not having any luck going through testing to
>> verify it's actually failing over between the connections.
>>
>> # multipath -l
>> mpath0 (30690a018f015191a6472441d1500f057)
>> [size=4 GB][features="0"][hwhandler="0"]
>> \_ round-robin 0 [active]
>>  \_ 3:0:0:0 sdc 8:32 [active][ready]
>> \_ round-robin 0 [enabled]
>>  \_ 1:0:1:0 sdb 8:16 [active][ready]
>>
>> I can unplug the HBA (see below) and the connection to the SAN remains.
>>
>> # multipath -l
>> mpath0 (30690a018f015191a6472441d1500f057)
>> [size=4 GB][features="0"][hwhandler="0"]
>> \_ round-robin 0 [active]
>>  \_ 3:0:0:0 sdc 8:32 [active][ready]
>> \_ round-robin 0 [enabled]
>>  \_ 1:0:1:0 sdb 8:16 [failed][faulty]
>>
>> But when I unplug the NIC connection, the multipath command hands,
>> trying to list files on the SAN partition hangs, and I'm getting these
>> messages:
>>
>> Nov 19 17:15:13 ems1 kernel: iscsi-sfnet:host3: Connect failed with rc
>> -113: No route to host
>> Nov 19 17:15:13 ems1 kernel: iscsi-sfnet:host3: establish_session
>> failed. Could not connect to target
>> Nov 19 17:15:13 ems1 kernel: iscsi-sfnet:host3: Waiting 10 seconds
>> before next login attempt
>>
>> How to troubleshoot this situation?
> 
> The IO is hanging waiting for the connection to be reestablished. 
> 
> You may need to set ConnFailTimeout to a non-zero value as indicated in
> http://people.redhat.com/mchristi/iscsi/RHEL4/doc/readme
> 

Mike Anderson is right. If you are using multipath you should set 
ConnFailTimeout to a low value like 3 or 5 seconds, because we want to 
fail commands quickly to the multipath layer. For dm-multipath you want 
to then set no_path_retry to either queue IO forever (or until the paths 
come back), or to some timeout.