Veritas Volume Manager 5.0 Migration Guide, HP-UX 11i v3, First Edition, May 2008

9VxVM and LVM
Introducing Veritas Volume Manager
■ Mirrored stripes (RAID-0 + RAID-1) and striped mirrors (RAID-1 +
RAID-0) combine the benefits of striping to improve performance by
spreading data 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.