VERITAS Volume Manager 5.0 Migration Guide (September 2006)

9VxVM and LVM
Introducing Veritas Volume Manager
across multiple disks, and mirroring to provide redundancy of data. Striped
mirror volumes are more tolerant of disk failure and have a shorter recovery
time than mirrored stripe volumes. Refer to the Veritas Volume Manager
Administrator’s Guide for more detailed information on these layouts.
■ Hot-relocation, which allows a system to react automatically to I/O failures on
redundant (mirrored or RAID-5) VxVM objects, restoring 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 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, to change RAID-5 to a mirrored layout
or to change a stripe unit size. The volume data remains available during the
relayout.
■ Improved RAID-5 subdisk, using layered volume technology where the RAID-5
subdisk move operation leaves the old subdisk in place while the new one is
being synchronized, thus maintaining redundancy and resiliency to failures
during the move.
Note: For more information on LVM, refer to HP-UX Managing Systems and
Workgroups, and LVM manual pages in HP-UX Reference Volumes 2, 3, and 5. For
information on VxVM commands, refer to the Veritas Volume Manager documentation.