Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Chapter 1, Understanding VERITAS Volume Manager

Volume Layouts in VxVM

Mirroring (RAID-1)

Mirroring uses multiple mirrors (plexes) to duplicate the information contained in a

volume. In the event of a physical disk failure, the plex on the failed disk becomes

unavailable, but the system continues to operate using the unaffected mirrors.

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 209 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 216 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.

The figure, “Mirrored-Stripe Volume Laid out on Six Disks” on page 26 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.