VERITAS Volume Manager 3.1 Administrator's Guide

Introduction to Volume Manager

Virtual Object Data Organization (Volume Layouts)

Chapter 1 45

RAID-5 volumes keep a copy of the data and calculated parity in a plex

that is “striped” across multiple disks. In the event of a disk failure, a

RAID-5 volume uses parity to reconstruct the data. It is possible to mix

concatenation and striping in the layout.

RAID-5 volumes can do logging to minimize recovery time. RAID-5

volumes use RAID-5 logs to keep a copy of the data and parity currently

being written. RAID-5 logging is optional and can be created along with

RAID-5 volumes or added later.

Figure 1-14, Parity Locations in a RAID-5 Model, shows parity locations

in a RAID-5 array conﬁguration. Every stripe has a column containing a

parity stripe unit and columns containing data. The parity is spread over

all of the disks in the array, reducing the write time for large

independent writes because the writes do not have to wait until a single

parity disk can accept the data.

Figure 1-14 Parity Locations in a RAID-5 Model

For more information, see “Volume Manager and RAID-5”.

Mirroring (RAID-1)

NOTE You may need an additional license to use this feature.

Mirroring

uses multiple mirrors (plexes) to duplicate the information

contained in a volume. In the event of a physical disk failure, the plex on

the failed disk becomes unavailable, but the system continues to operate

using the unaffected mirrors. Although a volume can have a single plex,

at least two plexes are required to provide redundancy of data. Each of

these plexes must contain disk space from different disks to achieve

D = Data Stripe Unit

P = Parity Stripe Unit

Stripe 1

Stripe 2

Stripe 3

Stripe 4