A
volume's layout refers to the organization of plexes in a volume.
Volume layout is the way plexes are configured to remap the volume
address space through which I/O is redirected at run-time. Volume
layouts are based on the concept of disk spanning, which is the
ability to logically combine physical disks in order to store data
across multiple disks.
A
variety of volume layouts are available, and each layout has
different advantages and disadvantages. The layouts that you choose
depend on the levels of performance and reliability required by your
system.
With
Volume Manager, you can change the volume layout without disrupting
applications or file systems that are using the volume. A volume
layout can be configured, reconfigured, resized, and tuned while the
volume remains accessible.
Common
volume layouts include:
- Concatenated
- Striped
- Mirrored
- RAID-5
- Layered
Concatenated
In
a concatenated volume, 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.
Striped
In
a striped volume, data is spread evenly across multiple disks.
Stripes are equally-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.
Mirrored
A
mirrored volume uses multiple plexes to 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.
RAID-5
A
RAID-5 volume 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.
Layered
A
layered volume is a virtual Volume Manager object that nests volumes
within volumes to create more complex volume structures that mirror
data at a more granular level.
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