VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Types of Volume Layouts
160 VERITAS Volume Manager Administrator’s Guide
◆ Mirrored—A volume with multiple data plexes that duplicate the information
contained in a volume. Although a volume can have a single data plex, at least two
are required for true mirroring to provide redundancy of data. For the redundancy to
be useful, eachof these data plexesshould containdisk space fromdifferentdisks. For
more information, see “Mirroring (RAID-1)” on page 21.
◆ 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 tomirroring, the use of parity toimplement dataredundancy reducesthe
amount of space required. For more information, see “RAID-5 (Striping with Parity)”
on page 25.
◆ Mirrored-stripe—A volume that is configured as a striped plex and another plex 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). The
advantages of this layout are increased performance by spreading data across
multiple disks and redundancy of data. “Striping Plus Mirroring (Mirrored-Stripe or
RAID-0+1)” on page 21.
◆ Layered Volume—A volume constructed from other volumes. Non-layered volumes
are constructed by mapping their subdisks to VM disks. Layered volumes are
constructed by mapping their subdisks to underlying volumes (known as storage
volumes), and allow the creation of more complex forms of logical layout. For more
information, see “Layered Volumes” on page 30.
Examples of layered volumes are striped-mirror and concatenated-mirror volumes.
Note The VERITAS Enterprise Administrator (VEA) terms a striped-mirror volume as
Striped-Pro, and a concatenated- mirror volume as Concatenated-Pro.
A striped-mirror volume is created by configuring several mirrored volumes as the
columns of a striped volume. This layout offers the same benefits as a non-layered
mirrored-stripe volume. In addition it provides faster recovery as the failure of single
diskdoes notforce an entirestriped plex offline.For moreinformation, see “Mirroring
Plus Striping (Striped-Mirror, RAID-1+0 or RAID-10)” on page 22.
A concatenated-mirror volume is created by concatenatingseveral mirrored volumes.
This provides faster recovery as the failure of a single disk does not force the entire
mirror offline.