VERITAS Volume Manager 3.1 Administrator's Guide

Volume Manager Operations
Creating Volumes
Chapter 392
traffic areas exist on certain subdisks.
• RAID-5—A volume that uses striping to spread data and parity
evenly across multiple disks in an array. Each stripe contains a parity
stripe unit and data stripe units. Parity can be used to reconstruct
data if one of the disks fails. In comparison to the performance of
striped volumes, write throughput of RAID-5 volumes decreases since
parity information needs to be updated each time data is accessed.
However, in comparison to mirroring, the use of parity reduces the
amount of space required.
• Mirrored—A volume with multiple plexes that duplicate the
information contained in a volume. Although a volume can have a
single plex, at least two are required for true mirroring (redundancy
of data). Each of these plexes should contain disk space from different
disks, for the redundancy to be useful.
• Striped and Mirrored—Avolume with a striped plex and anotherplex
that mirrors the striped one. This requires at least two disks for
striping and one or more other disks for mirroring (depending on
whether the plex is simple or striped). A striped and mirrored volume
is advantageous because it both spreads data across multiple disks
and provides redundancy of data.
• Mirrored and Striped—A volume with a plex that is mirrored and
another plex that is striped. The mirrored and striped layout offers
the benefits of spreading data across multiple disks (striping) while
providing redundancy (mirroring) of data. The mirror and its striped
plex are allocated from separate disks.
• Layered Volume—A volume built on top of volumes. Layered volumes
can be constructed by mapping a subdisk to a VM disk or to a
storage volume. A storage volume provides a recursive level of layout
that is similar to the top-level volumes. Layered volumes allow for
more combinations of logical layouts.