Virtual Disk Backend Options

Different options can be specified when exporting a virtual disk backend. These options are indicated in the options= argument of the ldm add-vdsdev command as a comma separated list. The valid options are: ro, slice, and excl.

Read-only (ro) Option

The read-only (ro) option specifies that the backend is to be exported as a read-only device. In that case, the virtual disk assigned to the guest domain can only be accessed for read operations, and any write operation to the virtual disk will fail.

Exclusive (excl) Option

The exclusive (excl) option specifies that the backend in the service domain has to be opened exclusively by the virtual disk server when it is exported as a virtual disk to another domain. When a backend is opened exclusively, it is not accessible by other applications in the service domain. This prevents the applications running in the service domain from inadvertently using a backend that is also being used by a guest domain.

Some drivers do not honor the excl option and will disallow some virtual disk backends from being opened exclusively. The excl option is known to work with physical disks and slices, but the option does not work with files. It may or may not work with pseudo devices, such as disk volumes. If the driver of the backend does not honor the exclusive open, the backend excl option is ignored, and the backend is not opened exclusively.

Because the excl option prevents applications running in the service domain from accessing a backend exported to a guest domain, do not set the excl option in the following situations:

• When guest domains are running, if you want to be able to use commands such as format(1M) or luxadm(1M) to manage physical disks, then do not export these disks with the excl option.

• When you export an SVM volume, such as a RAID or a mirrored volume, do not set the excl option. Otherwise, this can prevent SVM from starting some recovery operation in case a component of the RAID or mirrored volume fails. See Using Virtual Disks on Top of SVM for more information.

• If the Veritas Volume Manager (VxVM) is installed in the service domain and Veritas Dynamic Multipathing (VxDMP) is enabled for physical disks, then physical disks have to be exported without the (non-default) excl option. Otherwise, the export fails, because the virtual disk server (vds) is unable to open the physical disk device. See Using Virtual Disks When VxVM Is Installed for more information.

• If you are exporting the same virtual disk backend multiple times from the same virtual disk service, see Export a Virtual Disk Backend Multiple Times for more information.

By default, the backend is opened non-exclusively. That way the backend still can be used by applications running in the service domain while it is exported to another domain. Note that this is a new behavior starting with the Solaris 10 5/08 OS release. Prior to the Solaris 10 5/08 OS release, disk backends were always opened exclusively, and it was not possible to have a backend opened non-exclusively.

Slice (slice) Option

A backend is normally exported either as a full disk or as a single slice disk depending on its type. If the slice option is specified, then the backend is forcibly exported as a single slice disk.

This option is useful when you want to export the raw content of a backend. For example, if you have a ZFS or SVM volume where you have already stored data and you want your guest domain to access this data, then you should export the ZFS or SVM volume using the slice option.

For more information about this option, see Virtual Disk Backend.