Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

228 Creating volumes

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 35.

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 38.

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 42.

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 45.

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 42.