Performance Tuning

When a program or device uses too much disk I/O, bottlenecks can occur, creating a hot spot and degrading performance. You can make adjustments by moving subdisks from an area of high I/O usage to another disk that has lower usage.

The VxVM statistics function provides I/O statistics to allow you to do performance tuning to improve overall disk and system performance.

You can improve disk and system performance by identifying I/O bottlenecks, or hot spots; then moving data among physical drives to evenly balance the I/O load among the disk drives. This is known as load balancing.

Real-time Statistics Collection and Display

To set up real-time statistics collection and display, you need to “Select Online Display Options”.

Select Online Display Options

Use the following procedure to set the display options.

Procedure 2-3 To select the online data display options:

Choose Tools > Statistics > Online Data Display Options to bring up the Online Display Options window.
Select the checkboxes for the required statistics parameters.
- Read Requests/Second
  The number of read requests per second for selected storage objects.
- Write Requests/Second
  The number of write requests per second for selected storage objects.
- Read Blocks/Second
  The amount of read request data (in blocks per second) that is processed for selected storage objects. It is the throughput on the read requests made.
- Write Blocks/Second
  The amount of write request data (in blocks per second) that is processed for selected storage objects. It is the throughput on the write requests made.
- Avg Time (microseconds)/Read Block
  The average time in microseconds that it takes to process a read block from the time a request is made until the data is returned.
- Avg Time (microseconds)/Write Block
  The average time in microseconds that it takes to process a read block from the time a request is made until the data is returned.
By default, all the statistical parameters will be enabled.
Set I/O Refresh Rate/Sec.
This is the time interval of the refresh of the data collection screen display. The program continuously runs the actual statistics in the background, but changes the display of them on the Online Monitoring according to the refresh rate you set.
Set Threshold.
The Threshold is the minimum amount of I/O per second that a disk or subdisk has to have to display a color other than blue. Blue is the lowest state, Low I/O activity. The default threshold is 15.
Set Hot spot indicator based on category.
When you are finished with your changes, click OK.

Viewing Real-Time Statistics

You can view real-time statistics in the Volume to Disk Mapping Window. By default, the Volume to Disk Mapping Window comes up with statistics collection switched off. To turn it on, you need to:

Select the disk group to be monitored
Select Actions > Disk/Vol Map
Select:
- View > Collect Statistics
  Statistics are accumulated from when they were reset (usually they are reset when the system boots/reboots, or at object creation, whichever is most recent).
- View > Compare on Refresh
  Each statistic request is compared with the last one to determine where the current high I/O activity is occurring.

Monitoring Performance

You can change the criteria that determine which disks are displayed as slow performers. Select View > Perf. Monitoring Parameters and complete the Performance Monitoring Parameters dialog box. This dialog box allows you to configure how many disks are shown as slowest and next slowest performers, the sampling interval, and whether to show the slowest performers for reading, for writing, or for both reading and writing.

Performance Tuning

Technical documentation

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Real-time Statistics Collection and Display

Select Online Display Options

Viewing Real-Time Statistics

Monitoring Performance