Not able to load or install a DomU (Guest machine) using a disk from Multipath

This document (7011590) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 11 Service Pack 2

Situation

If you have multipath running in SLES 11 SP2 Xen Host and the VM is using multipath disk, it will fail to load during the installation after the first boot.

It will also happen if you have migrated your Xen Host server from SLES 11 SP1 to SLES 11 SP2. After migration the VM installed in SLES 11 SP1 you will not boot in SLES 11 SP2.

When the issue happens you will see an error on the screen similar to that during the VM boot:

"Waiting for device /dev/xvda3 to appear: ................... Could not find /dev/xvda3"

For Windows VM the Windows start screen will freeze and you can only power off the VM using virt-manager.

Resolution

Follow the steps below and the VM will be able to use the multipath disk.

1 - Using multipath -ll command, find the WWID from the disk that your VM is using:

# multipath -ll
149455400000000000000000001000000161312000300a00c dm-7 IET,VIRTUAL-DISK
size=37G features='1 no_partitions' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=1 status=active
| `- 10:0:0:4 sdj 8:144 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
`- 11:0:0:4 sdl 8:176 active ready running
14945540000000000000000000100000001f711000300a00c dm-3 IET,VIRTUAL-DISK
size=37G features='1 no_partitions' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=1 status=active
| `- 10:0:0:0 sdb 8:16 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
`- 11:0:0:0 sdc 8:32 active ready running

2 - Add the WWID into the multipath.conf using the syntax bellow:

multipaths {
    multipath {
    wwid 149455400000000000000000001000000161312000300a00c
    features "1 no_partitions"
}
    multipath {
    wwid 14945540000000000000000000100000001f711000300a00c
    features "1 no_partitions"
   }
}

3 - Save the file and then restart multipath service # rcmultipathd restart. You can also reboot your server to validate these changes.

After that you will be able to finish your VM installation or boot the VM normally.

NOTE:
If you don't remember which disk your VM is using, you can find that information through the virt-manager or use the command # xm list -l <vm-name>

If your server is booting from SAN please do NOT add the disk used to boot your server.

Cause

Xen requires exclusive access to protect disk from another VM, so nobody can create two VMs using same disk by default.
To protect the data in SLES 11 SP2 the no_partition feature will hide the partitions from the host and it will allow the VM to be loaded.

Additional Information

Disclaimer

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