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

Chapter 15, Performance Monitoring and Tuning
Performance Guidelines
401
Combining Mirroring and Striping
Note You need a full license to use this feature.
Mirroring and striping can be used together to achieve a significant improvement in
performance when there are multiple I/O streams.
Striping provides better throughput because parallel I/O streams can operate
concurrently on separate devices. Serial access is optimized when I/O exactly fits across
all stripe units in one stripe.
Because mirroring is generally used to protect against loss of data due to disk failures, it is
often applied to write-intensive workloads which degrades throughput. In such cases,
combining mirroring with striping delivers both high availability and increased
throughput.
A mirrored-stripe volume may be created by striping half of the available disks to form
one striped data plex, and striping the remaining disks to form the other striped data plex
in the mirror. This is often the best way to configure a set of disks for optimal performance
with reasonable reliability. However, the failure of a single disk in one of the plexes makes
the entire plex unavailable.
Alternatively, you can arrange equal numbers of disks into separate mirror volumes, and
then create a striped plex across these mirror volumes to form a striped-mirror volume
(see “Mirroring Plus Striping (Striped-Mirror, RAID-1+0 or RAID-10)” on page 26). The
failure of a single disk in a mirror does not take the disks in the other mirrors out of use. A
striped-mirror layout is preferred over a mirrored-stripe layout for large volumes or large
numbers of disks.
RAID-5
Note You need a full license to use this feature.
RAID-5 offers many of the advantages of combined mirroring and striping, but requires
less disk space. RAID-5 read performance is similar to that of striping and RAID-5 parity
offers redundancy similar to mirroring. Disadvantages of RAID-5 include relatively slow
write performance.
RAID-5 is not usually seen as a way of improving throughput performance except in cases
where the access patterns of applications show a high ratio of reads to writes.