Re: [libvirt-users] libvirt does not recognize all devices in iscsi and mpath pools in a predictable manner

Hi, I'm using libvirt 0.8.3 on Fedora 14 (as I wrote earlier, I'm having some trouble updating to the newest version), and I'm having problems getting iscsi and mpath storage pools to work in a usable and consistent manner. I have two storage pools defined on the host machine, one for raw iscsi- devices and one for those same iscsi devices device-mapped by multipath. They look like this: <pool type='iscsi'> <name>iscsi01</name> <source> <host name='10.3.1.15'/> <device path='iqn.1984-05.com.dell:powervault.md3200i.6782bcb0000859f3000000004d3eec7d'/> </source> <target> <path>/dev/disk/by-id</path> </target> </pool> and: <pool type="mpath"> <name>mpath01</name> <target> <path>/dev/mapper</path> </target> </pool> I chose <path>/dev/disk/by-id</path> over /dev/disk/by-path for the iscsi pool because I need to be able to migrate running virtual machines to other hosts, so the actual device paths for the disks need to be the same on all hosts in the cluster.

I have two LUNs configured in the iSCSI array, and when I list the volumes in the iscsi pool, I get this: virsh # vol-list iscsi01 Name Pfad ----------------------------------------- 23.0.0.1 /dev/disk/by-id/wwn-0x6782bcb0000859f3000007004e680190 23.0.0.2 /dev/disk/by-id/scsi-36782bcb0000859f3000007294e6e73f2 Apparently, for some weird reason, libvirt chooses one naming scheme for one of the volumes and another for the other one. This a problem for me for two reasons. 1 - Once I create a new lun for a new VM, rescan the iscsi bus and refresh libvirt's pool (see my mail from 24th of August on this list), I need to be able to automatically and reliably identify the corresponding new volumes in libvirt's volume list, so I can initialize them by copying an OS image onto them and then assign them to the new virtual machine. This is made a lot harder if libvirt randomly switches between naming schemes - though still feasible if I'm aware of the problem. 2 - I need to be able to migrate running VMs to a different host machine, in case the current one is overloaded or in need of maintenance. This is bound to be problematic if the storage volumes go by different path names on the different hosts.

Both LUNs do appear under both naming schemes under /dev/disk/by-id: ls /dev/disk/by-id/ [...] scsi-36782bcb0000859f3000007004e680190 [...] scsi-36782bcb0000859f3000007294e6e73f2 scsi-36a4badb00b0f910012e0fccb07606fe6 [...] wwn-0x6782bcb0000859f3000007004e680190 [...] wwn-0x6782bcb0000859f3000007294e6e73f2 wwn-0x6a4badb00b0f910012e0fccb07606fe6 [...] (snipped some irrelevant parts)

With the mpath pool, it's even worse: One of the two volumes is completely missing: virsh # vol-list mpath01 Name Pfad ----------------------------------------- dm-3 /dev/mapper/36782bcb0000859f3000007004e680190 Both iscsi volumes have in fact been picked up by multipathd and do appear in /dev/mapper/, too, but no matter how often I say refresh-pool mpath01, it will always only show the one volume.