Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Types of Volume Layouts
196 VERITAS Volume Manager Administrator’s Guide
Types of Volume Layouts
VxVM allows you to create volumes with the following layout types:
◆ Concatenated—A volume whose subdisks are arranged both sequentially and
contiguously within a plex. Concatenation allows a volume to be created from
multiple regions of one or more disks if there is not enough space for an entire volume
on a single region of a disk. For more information, see “Concatenation and Spanning”
on page 18.
◆ Striped—A volume with data spread evenly across multiple disks. Stripes are
equal-sized fragments that are allocated alternately and evenly to the subdisks of a
single plex. There must be at least two subdisks in a striped plex, each of which must
exist on a different disk. Throughput increases with the number of disks across which
a plex is striped. Striping helps to balance I/O load in cases where high traffic areas
exist on certain subdisks. For more information, see “Striping (RAID-0)” on page 21.
◆ 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, each of these data plexes should contain disk space from different disks. For
more information, see “Mirroring (RAID-1)” on page 25.
◆ 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 to implement data redundancy reduces the
amount of space required. For more information, see “RAID-5 (Striping with Parity)”
on page 29.
◆ 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 25.
◆ 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. Examples of
layered volumes are striped-mirror and concatenated-mirror volumes. For more
information, see “Layered Volumes” on page 34.