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

45Understanding Veritas Volume Manager

Volume layouts in VxVM

Figure 1-22 Veritas Volume Manager RAID-5 array

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

See “Creating a RAID-5 volume” on page 248 for information on how to create a RAID-5

volume.

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 unit is located in the next

stripe, shifted left one column from the previous parity stripe unit location. If there are

more stripes than columns, the parity stripe unit placement begins in the rightmost column

again.

Figure 1-23 shows a left-symmetric parity layout with five disks (one per column).

Column 0 Column 1 Column 2 Column 3

SD SD

SD = subdisk

Stripe 1

Stripe 2