Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

physical disk. The combination of a volume layout and the physical disks therefore
determines the storage service available from a given virtual device.
Layered volumes
A layered volume is constructed by mapping its subdisks to underlying volumes.
The subdisks in the underlying volumes must map to VM disks, and hence to
attached physical storage.
Layered volumes allow for more combinations of logical compositions, some of
which may be desirable for configuring a virtual device. For example, layered
volumes allow for high availability when using striping. Because permitting free
use of layered volumes throughout the command level would have resulted in
unwieldy administration, some ready-made layered volume configurations are
designed into VxVM.
See “Layered volumes” on page 49.
These ready-made configurations operate with built-in rules to automatically
match desired levels of service within specified constraints. The automatic
configuration is done on a “best-effort” basis for the current command invocation
working against the current configuration.
To achieve the desired storage service from a set of virtual devices, it may be
necessary to include an appropriate set of VM disks into a disk group, and to
execute multiple configuration commands.
To the extent that it can, VxVM handles initial configuration and on-line
re-configuration with its set of layouts and administration interface to make this
job easier and more deterministic.
Layout methods
Data in virtual objects is organized to create volumes by using the following layout
methods:
■ Concatenation, spanning, and carving
See “Concatenation, spanning, and carving” on page 36.
■ Striping (RAID-0)
See “Striping (RAID-0)” on page 38.
■ Mirroring (RAID-1)
See “Mirroring (RAID-1)” on page 41.
■ Striping plus mirroring (mirrored-stripe or RAID-0+1)
See “Striping plus mirroring (mirrored-stripe or RAID-0+1)” on page 42.
■ Mirroring plus striping (striped-mirror, RAID-1+0 or RAID-10)
35Understanding Veritas Volume Manager
Volume layouts in VxVM