HP Veritas Volume Manager 5.0 -UX 11i v3 Performance monitoring, Obtaining performance data, Setting performance priorities

Performance monitoring and tuning 467

Performance monitoring

Note: To improve performance for read-intensive workloads, you can attach up to 32 data plexes to the same volume. However, this would usually be 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.

Best performance is usually achieved by striping and mirroring all volumes across a reasonable number of disks and mirroring between controllers, when possible. This procedure tends to even out the load between all disks, but it can make VxVM more difficult to administer. For large numbers of disks (hundreds or thousands), set up disk groups containing 10 disks, where each group is used to create a striped-mirror volume. This technique provides good performance while easing the task of administration.

Obtaining performance data

VxVM provides two types of performance information: I/O statistics and I/O traces. Each of these can help in performance monitoring. You can obtain I/O statistics using the vxstat command, and I/O traces using the vxtrace command. A brief discussion of each of these utilities may be found in the following sections.