CentOS - Mar 2008 - Device-mapper-multipath not working correctly with GNBD devices

Hi all,

 

I am trying to configure a failover multipath between 2 GNBD devices.

 

I have a 4 nodes Redhat Cluster Suite (RCS) cluster. 3 of them are used for
running services, 1 of them for central storage. In the future I am going to
introduce another machine for central storage. The 2 storage machine are
going to share/export the same disk. The idea is not to have a single point
of failure on the machine exporting the storage.

 

For concept testing I am using one machine on which I have configured 2 GNBD
exports, which are exporting exactly the same disk. These are configured
with:

 

# /sbin/gnbd_export -d /dev/sdb1 -e gnbd0 -u gnbd

# /sbin/gnbd_export -d /dev/sdb1 -e gnbd1 -u gnbd

 

They are exporting with the same id, so the multipath driver will
automatically configure them as alternative paths to the same storage.

 

Now on one of the cluster nodes used for running services I am importing
these GNBD devices with:

 

# /sbin/gnbd_import -i gnbd1

 

where gnbd1 is the hostname of the machine exporting the GNBD devices.

 

And I have these imported ok:

 

# gnbd_import -l

Device name : gnbd1

----------------------

    Minor # : 0

 sysfs name : /block/gnbd0

     Server : gnbd11

       Port : 14567

      State : Open Connected Clear

   Readonly : No

    Sectors : 41941688

 

Device name : gnbd0

----------------------

    Minor # : 1

 sysfs name : /block/gnbd1

     Server : gnbd1

       Port : 14567

      State : Open Connected Clear

   Readonly : No

    Sectors : 41941688

 

#

 

After, I have configured the device-mapper multipath by commenting the
"blacklist" section in /etc/multipath.conf and adding this
"defaults"
section:

 

defaults {

        user_friendly_names yes

        polling_interval 5

        #path_grouping_policy failover

        path_grouping_policy multibus

        rr_min_io 1

        failback immediate

        #failback manual

        no_path_retry fail

        #no_path_retry queue

}

 

Now I have the mpath device configured correctly (IMHO):

 

# multipath -ll

mpath0 (gnbd) dm-2 GNBD,GNBD

[size=20G][features=0][hwhandler=0]

\_ round-robin 0 [prio=2][enabled]

 \_ #:#:#:# gnbd0 252:0 [active][ready]

 \_ #:#:#:# gnbd1 252:1 [active][ready]

#

 

# dmsetup ls

mpath0 (253, 2)

VolGroup00-LogVol01 (253, 1)

VolGroup00-LogVol00 (253, 0)

#

 

Now I mkfs.ext3 over the mpath0 device to create a filesystem, then mount.
After I start to copy a file (with scp - to have a progress bar) and during
the copy process I shutdown one of the exported GNBD device on the disk
exporting machine with:

 

# gnbd_export -r gnbd1 -O

 

After a while in the maillog:

 

gnbd_recvd[3357]: client lost connection with gnbd11 : Broken pipe

gnbd_recvd[3357]: reconnecting

kernel: gnbd1: Receive control failed (result -32)

kernel: gnbd1: shutting down socket

kernel: exiting GNBD_DO_IT ioctl

kernel: gnbd1: Attempted send on closed socket

gnbd_recvd[3357]: ERROR [gnbd_recvd.c:292] login refused by the server : No
such

device

gnbd_recvd[3357]: reconnecting

kernel: device-mapper: multipath: Failing path 252:1.

multipathd: gnbd1: directio checker reports path is down

multipathd: checker failed path 252:1 in map mpath0

multipathd: mpath0: remaining active paths: 1

gnbd_recvd[3357]: ERROR [gnbd_recvd.c:292] login refused by the server : No
such

device

gnbd_recvd[3357]: reconnecting

 

Now the copy process is freezed. It stays that way until the GNBD device is
exported again. I try some commands on the multipath machine:

 

# multipath -ll

gnbd1: checker msg is "directio checker reports path is down"

mpath0 (gnbd) dm-2 GNBD,GNBD

[size=20G][features=0][hwhandler=0]

\_ round-robin 0 [prio=1][active]

 \_ #:#:#:# gnbd0 252:0 [active][ready]

 \_ #:#:#:# gnbd1 252:1 [failed][faulty]

<freezed, the prompt is not returning back>

 

This prompt get back after the GNBD device is exported again.

 

My expectations were that in such a scenario the multipath driver is going
to switch the requests to the other path and everything should continue to
work. Am I wrong?

 

I have upgraded to the last version of all the RPMs. I am using CentOS 5.1.

 

I have tried different multipath settings (which are commented out in the
multipath.conf "defaults" section I pasted previously), but nothing
happens.

 

 

This may be useful. When starting the machine in the log:

 

multipathd: gnbd0: add path (uevent)

kernel: device-mapper: multipath round-robin: version 1.0.0 loaded

multipathd: mpath0: load table [0 41941688 multipath 0 0 1 1 round-robin 0 1
1

252:0 1000]

multipathd: mpath0: event checker started

multipathd: dm-2: add map (uevent)

multipathd: dm-2: devmap already registered

gnbd_recvd[3357]: gnbd_recvd started

kernel: resending requests

multipathd: gnbd1: add path (uevent)

multipathd: mpath0: load table [0 41941688 multipath 0 0 1 1 round-robin 0 2
1

252:0 1000 252:1 1000]

multipathd: dm-2: add map (uevent)

multipathd: dm-2: devmap already registered

 

 

Maybe this is a bug of GNBD not the multipath? Any help for getting this
working will be very appreciated.

 

Thanks.

 

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