VERITAS Volume Manager 3.5 Migration Guide (September 2004)

Chapter 1

VxVM and LVM

Introducing the VERITAS Volume Manager

The following VERITAS Volume Manager features require an additional license (product B9116AA):

• Dynamic Multipathing (DMP) for active-active devices, such as HP Surestore Disk Array xp256, HP

Surestore Disk System FC10 and other disk devices. DMP provides higher availability to data on disks

with multiple host-to-device pathways by providing a disk/device path failover mechanism. In the event of

a loss of one connection to a disk, the system continues to access the data over the other available

connections to the disk. DMP also provides in some cases, improved I/O performance from disks with

multiple concurrently available pathways by balancing the I/O load uniformly across multiple I/O paths

to the disk device. LVM supports path failover but does not support I/O balancing. 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 3.5 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.