Veritas Storage Foundation 5.1 SP1 Advanced Features Administrator"s Guide (5900-1503, April 2011)

to a disk is lost, the system continues to access the data over the other available
connections to the disk.
DMP can also provide improved I/O performance from disks with multiple
pathways that are concurrently available. DMP can balance the I/O load
uniformly across the multiple paths to the disk device.
DMP can coexist with the native multi-pathing functionality that is provided
in HP-UX 11i Version 3.
DMP also supports the new persistent device file names in addition to legacy
device file names and enclosure-based names.
■ Free Space Management, providing simple goal-based allocation of storage.
■ Task Monitor, which tracks the progress of system recovery by monitoring
task creation, maintenance, and completion. The Task Monitor lets you pause,
resume, and stop as desired to adjust the impact on system performance.
■ Multiple mirroring with up to 32 mirror copies of a volume’s address space.
■ Mirrored stripes (RAID-0 + RAID-1) and striped mirrors (RAID-1 + RAID-0)
combine the benefits of striping and mirroring. These layouts improve
performance by spreading data across multiple disks, and provide redundancy
of data by mirroring. Striped mirror volumes are more tolerant of disk failure
and have a shorter recovery time than mirrored stripe volumes. More detailed
information is available on these layouts.
See Veritas Volume Manager Administrator’s Guide.
■ Hot-relocation, which allows a system to react automatically to I/O failures
on redundant (mirrored or RAID-5) VxVM objects. This feature restores
redundancy and access to those objects without administrative intervention.
VxVM detects I/O failures on objects and relocates the affected subdisks. The
vxunreloc utility can be used to restore the system to the same configuration
that existed before the disk failure.
■ RAID-5, which provides data redundancy by using parity, at a lower storage
cost than mirroring. RAID-5 provides data redundancy by using parity. Parity
is a calculated value used to reconstruct data after a failure. While data is being
written to a RAID-5 volume, parity is calculated by doing an exclusive OR (XOR)
procedure on the data. The resulting parity is then written in an interleaved
fashion to the RAID-5 array that is established by the volume. If a portion of
a RAID-5 volume fails, the data that was on that portion of the failed volume
can be recreated from the remaining data and parity information.
■ Online Data Migration, which allows for regions of storage on physical media
to be dynamically moved to other physical devices.
■ Online Relayout or Dynamic Restriping, the ability to change logical data
configuration while online. For example, use this feature to change RAID-5 to
393Offline data migration
About VxVM and LVM