Dynamic Path Selection

Language:

You can dynamically select the path to be used for a virtual disk on guest domains and alternate domains that run at least the Oracle Solaris 11.2 SRU 1 OS. The control domain must run at least the Oracle Solaris 11.2 SRU 8 OS and at least the Oracle VM Server for SPARC 3.2 software.

Dynamic path selection occurs when the first path in an mpgroup disk is changed by using the ldm set-vdisk command to set the volume property to a value in the form volume-name@service-name. An active domain that supports dynamic path selection can switch to only the selected path. If the updated drivers are not running, this path is selected when the Oracle Solaris OS reloads the disk instance or at the next domain reboot.

The dynamic path selection feature enables you to dynamically perform the following steps while the disk is in use:

Specify the disk path to be tried first by the guest domain when attaching the disk
Change the currently active path to the one that is indicated for already attached multipathing disks

Using the ldm add-vdisk command with an mpgroup disk now specifies the path indicated by volume-name@service-name as the selected path with which to access the disk.

The selected disk path is listed first in the set of paths provided to the guest domain irregardless of its rank when the associated mpgroup was created.

You can use the ldm set-vdisk command on bound, inactive, and active domains. When used on active domains, this command permits you to choose only the selected path of the mpgroup disk.

The ldm list-bindings command shows the following information:

The STATE column for each mpgroup path indicates one of the following values:
- active – Current active path of the mpgroup
- standby – Path is not currently used
- unknown – Domain does not support dynamic path selection, the device is not attached, or an error prevents the path state from being retrieved
The disk paths are listed in the order that is used for choosing the active path
The volume that is associated with the disk is the selected path for the mpgroup and is listed first.

The following example shows that the selected path is vol-ldg2@opath-ldg2 and that the currently used active path is going through the ldg1 domain. You might see this situation if the selected path could not be used and the second possible path was used instead. Even if the selected path comes online, the non-selected path continues to be used. To make the first path active again, re-issue the ldm set-vdisk command to set the volume property to the name of the path you want.
```
DISK

NAME            VOLUME                  TOUT ID DEVICE SERVER  MPGROUP
disk            disk-ldg4@primary-vds0       0  disk@0 primary
tdiskgroup      vol-ldg2@opath-ldg2          1  disk@1 ldg2    testdiskgroup
    PORT MPGROUP VOLUME        MPGROUP SERVER   STATE
    2    vol-ldg2@opath-ldg2   ldg2             standby
    0    vol-ldg1@opath-vds    ldg1             active
    1    vol-prim@primary-vds0 primary          standby
```

If you use the ldm set-vdisk command on an mpgroup disk of a bound domain that does not run at least the Oracle Solaris 11.2 SRU 1 OS, the operation changes the order of the path priorities and the new path can be used first during next disk attach or reboot or if the OBP needs to access it.