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

Figure 1-22

Veritas Volume Manager RAID-5 array

Stripe 1

Stripe 2

Column 0 Column 1 Column 2 Column 3

SD SD = subdiskSD

VxVM allows each column of a RAID-5 plex to consist of a different number of

subdisks. The subdisks in a given column can be derived from different physical

disks. Additional subdisks can be added to the columns as necessary. Striping is

implemented by applying the first stripe across each subdisk at the top of each

column, then applying another stripe below that, and so on for the length of the

columns. Equal-sized stripe units are used for each column. For RAID-5, the default

stripe unit size is 16 kilobytes.

See “Striping (RAID-0)” on page 38.

Note: Mirroring of RAID-5 volumes is not supported.

See “Creating a RAID-5 volume” on page 321.

Left-symmetric layout

There are several layouts for data and parity that can be used in the setup of a

RAID-5 array. The implementation of RAID-5 in VxVM uses a left-symmetric

layout. This provides optimal performance for both random I/O operations and

large sequential I/O operations. However, the layout selection is not as critical

for performance as are the number of columns and the stripe unit size.

Left-symmetric layout stripes both data and parity across columns, placing the

parity in a different column for every stripe of data. The first parity stripe unit is

located in the rightmost column of the first stripe. Each successive parity stripe

47Understanding Veritas Volume Manager

Volume layouts in VxVM