VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Chapter 12, Performance Monitoring and Tuning
Performance Guidelines
283
Combining Mirroring and Striping
Note You may need an additional 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 mirroringis generallyused to protect against lossof datadue todisk 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, andstriping the remaining disks to form the other striped data plex
in the mirror. This is oftenthe bestway toconfigure a set of disks for optimal performance
with reasonable reliability. However, thefailure of a single diskin oneof 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 22). The
failureof asingle disk in a mirrordoes nottake 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 may need an additional 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 notusuallyseen asaway ofimprovingthroughputperformanceexcept in cases
where the access patterns of applications show a high ratio of reads to writes.