VERITAS Volume Manager 4.1 Migration Guide

VxVM and LVM

Introducing the VERITAS Volume Manager

Chapter 1 3

DMP support may be used with devices that show improved performance when I/O is

balanced across the multiple paths such as xp256, EMC Symmetrix disk array, and other

OEM array devices.

• 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 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 4.1 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.