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

Figure 15-2 shows an example in which the read policy of the mirrored-stripe
volume labeled HotVol is set to prefer for the striped plex PL1.
Figure 15-2
Use of mirroring and striping for improved performance
Disk 2
HotVol
PL1 SD2
Lightly used
volume
HotVol
PL1 SD3
Lightly used
volume
HotVol
PL1 SD1
Lightly used
volume
Disk 1 Disk 3 Disk 4
HotVol
PL1 SD4
Lightly used
volume
The prefer policy distributes the load when reading across the otherwise
lightly-used disks in PL1, as opposed to the single disk in plex PL2. (HotVol is an
example of a mirrored-stripe volume in which one data plex is striped and the
other data plex is concatenated.)
To improve performance for read-intensive workloads, you can attach up to 32
data plexes to the same volume. However, this approach is usually an ineffective
use of disk space for the gain in read performance.
Performance monitoring
As a system administrator, you have two sets of priorities for setting priorities
for performance. One set is physical, concerned with hardware such as disks and
controllers. The other set is logical, concerned with managing software and its
operation.
Setting performance priorities
The important physical performance characteristics of disk hardware are the
relative amounts of I/O on each drive, and the concentration of the I/O within a
drive to minimize seek time. Based on monitored results, you can then move the
location of subdisks to balance I/O activity across the disks.
The logical priorities involve software operations and how they are managed.
Based on monitoring, you may choose to change the layout of certain volumes to
improve their performance. You might even choose to reduce overall throughput
to improve the performance of certain critical volumes. Only you can decide what
is important on your system and what trade-offs you need to make.
Performance monitoring and tuning
Performance monitoring
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