VERITAS Volume Manager 3.1 Migration Guide

VxVM and LVM

Introducing the VERITAS Volume Manager

Chapter 116

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).

VxVM supports the combination of mirroring and striping. When

used together on the same volume, mirroring plus striping offers the

beneﬁts of spreading data across multiple disks (striping), while

providing redundancy (mirroring) of data.

If in the near future you are planning on using this data in a

clustered environment as a shared disk group, you should use

mirrored stripes, because striped mirrors are not yet supported in a

clustered environment. Otherwise, for non-clustered environments,

use striped mirrors, since these offer a volume that is more tolerant of

disk failure; if a disk failure occurs, the recovery time is shorter for

striped mirrors. Refer to the VERITAS Volume Manager 3.1

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