Information Technology Reference
In-Depth Information
A physical block device (disk or LUN)—for example,
/dev/dsk/c1t48d0s2
■
A slice of a physical device or LUN—for example,
/dev/dsk/c1t48d0s0
■
A disk image file residing in UFS or ZFS—for example,
/path-to-filename
■
A ZFS volume—for example,
zfs create -V 100m ldoms/domain/test/zdisk0
creates the back-end
/dev/zvol/dsk/ldoms/domain/test/zdisk0
■
A volume created by Solaris Volume Manager (SVM) or Veritas Volume
Manager (VxVM)
■
A CD ROM/DVD or a file containing an ISO image
■
A virtual disk may be marked as read-only. It also can be made exclusive, mean-
ing that it can be given to only one domain at a time. This setting is available
for disks based on physical devices rather than files, but the same effect can be
provided for file back-ends by using ZFS clones. The advantages of ZFS—such as
advanced mirroring, checksummed data integrity, snapshots, and clones—can be
applied to both ZFS volumes and disk image files residing in ZFS. ZFS volumes
generally provide better performance, whereas disk image files provide simpler
management, including renaming, copying, or transmission to other servers.
In general, the best performance is provided by virtual disks backed by physical
disks or LUNs, and the best flexibility is provided by file-based virtual disks or
volumes, which can be easily copied, backed up, and, when using ZFS, cloned from
a snapshot. Different kinds of disk back-ends can be used in the same domain:
The system volume for a domain can use a ZFS or UFS file system back-end, while
disks used for databases or other I/O intensive applications can use physical disks.
Redundancy can be provided by using virtual disk multipathing in the guest
domain, with the same virtual disk back-end presented to the guest by different
service domains. This provides fault tolerance for service domain failure. A time-
out interval can be used for I/O failover if the service domain becomes unavailable.
The
ldm
command syntax for creating a virtual volume lets you specify an MPXIO
group. The following commands illustrate the process of creating a disk volume
back-end served by both a control domain and an alternate service domain:
#
ldm add-vdsdev mpgroup=
foo
\
/path-to-backend-from-primary/domain ha-disk@primary-vds0
#
ldm add-vdsdev mpgroup=
foo
\
/path-to-backend-from-alternate/domain ha-disk@alternate-vds0
#
ldm add-vdisk
ha-disk ha-disk@primary-vds0 myguest
Multipathing can also be provided from a single I/O domain with multiplexed I/O
(MPXIO), by ensuring that the domain has multiple paths to the same device—for
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