Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

VxVM can split volumes across multiple drives. This approach gives you a finer
level of granularity when you locate data. After you measure access patterns, you
can adjust your decisions on where to place file systems. You can reconfigure
volumes online without adversely impacting their availability.
Striping
Striping improves access performance by cutting data into slices and storing it
on multiple devices that can be accessed in parallel. Striped plexes improve access
performance for both read and write operations.
After you identify the most heavily-accessed volumes (containing file systems or
databases), you can increase access bandwidth to this data by striping it across
portions of multiple disks.
Figure 16-1 shows an example of a single volume (HotVol) that has been identified
as a data-access bottleneck.
Figure 16-1
Use of striping for optimal data access
Disk 2
HotVol
PL1 SD2
Lightly
used
volume
Disk 1
Another
volume
Coolvolume
Disk 3
HotVol
PL1 SD3
Home
directory
volume
Disk 4
HotVol
PL1 SD4
Less
important
volume
HotVol
PL1 SD1
This volume is striped across four disks. The remaining space on these disks is
free for use by less-heavily used volumes.
Mirroring
Mirroring stores multiple copies of data on a system. When you apply mirroring
properly, data is continuously available. Mirroring also protects against data loss
due to physical media failure. If the system crashes or a disk or other hardware
fails, mirroring improves the chance of data recovery.
In some cases, you can also use mirroring to improve I/O performance. Unlike
striping, the performance gain depends on the ratio of reads to writes in the disk
accesses. If the system workload is primarily write-intensive (for example, greater
than 30 percent writes), mirroring can reduce performance.
Performance monitoring and tuning
Performance guidelines
522