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

40 Understanding Veritas Volume Manager

Volume layouts in VxVM

Note: Although a volume can have a single plex, at least two plexes are required to

provide redundancy of data. Each of these plexes must contain disk space from different

disks to achieve redundancy.

When striping or spanning across a large number of disks, failure of any one of those disks

can make the entire plex unusable. Because the likelihood of one out of several disks

failing is reasonably high, you should consider mirroring to improve the reliability (and

availability) of a striped or spanned volume.

See “Creating a mirrored volume” on page 241 for information on how to create a

mirrored volume.

Disk duplexing, in which each mirror exists on a separate controller, is also supported. See

“Mirroring across targets, controllers or enclosures” on page 247 for details.

Striping plus mirroring (mirrored-stripe or RAID-0+1)

Note: You need a full license to use this feature.

VxVM supports the combination of mirroring above striping. The combined layout is

called a mirrored-stripe layout. A mirrored-stripe layout offers the dual benefits of striping

to spread data across multiple disks, while mirroring provides redundancy of data.

For mirroring above striping to be effective, the striped plex and its mirrors must be

allocated from separate disks.

Figure 1-17 shows an example where two plexes, each striped across three disks, are

attached as mirrors to the same volume to create a mirrored-stripe volume.

Figure 1-17 Mirrored-stripe volume laid out on six disks

See “Creating a mirrored-stripe volume” on page 246 for information on how to create a

mirrored-stripe volume.

Striped plex

Mirror

Mirrored-stripe

volume

Column 0 Column 1 Column 2