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

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 311.
See “Mirroring across targets, controllers or enclosures” on page 319.
Striping plus mirroring (mirrored-stripe or RAID-0+1)
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
Striped
plex
Mirror
column 0 column 1 column 2
column 0 column 1 column 2
Mirrored-stripe
volume
Striped
plex
See “Creating a mirrored-stripe volume” on page 318.
The layout type of the data plexes in a mirror can be concatenated or striped. Even
if only one is striped, the volume is still termed a mirrored-stripe volume. If they
are all concatenated, the volume is termed a mirrored-concatenated volume.
Understanding Veritas Volume Manager
Volume layouts in VxVM
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