Disk Activity Test

When executed on Windows, Solaris, AIX, and HP-UX systems, this test reports statistics pertaining to the input/output utilization of each physical disk on a system.

Target of the test : Any host system

Agent deploying the test : An internal/remote agent

Outputs of the test : One set of results for each host monitored

Configurable parameters for the test
  1. Test period - How often should the test be executed
  2. Host - The host for which the test is to be configured.
  3. useexe - Setting the USEEXE flag to true, ensures that the disk activity metrics are collected by executing a binary instead of dynamically linking to the Performance instrumentation library. By default, this is set to false.
  4. disks- To obtain disk activity metrics for both logical and physical disks, enter all in the DISKS text box. To collect metrics for physical disks, set the DISKS parameter to Physical and to collect metrics for logical disks, set the parameter to Logical.
  5. DETAILED DIAGNOSIS – This parameter does not apply to AIX hosts.
Measurements made by the test
Measurement Description Measurement Unit Interpretation

Disk busy:

Indicates the percentage of elapsed time during which the disk is busy processing requests (i.e., reads or writes).

Percent

Comparing the percentage of time that the different disks are busy, an administrator can determine whether the application load is properly balanced across the different disks.

Data read rate from disk:

Indicates the rate at which bytes are transferred from the disk during read operations.

KB/Sec

A very high value indicates an I/O bottleneck on the server.

Data write rate to disk:

Indicates the rate at which bytes are transferred from the disk during write operations.

KB/Sec

A very high value indicates an I/O bottleneck on the server.

Disk service time:

Indicates the average time that this disk took to service each transfer request ( i.e., the average I/O operation time)

Secs

A sudden rise in the value of this measure can be attributed to a large amount of information being input or output. A consistent increase however, could indicate an I/O processing bottleneck.

Disk queue time:

Indicates the average time that transfer requests waited idly on queue for this disk.

Secs

Ideally, the value of this measure should be low.

Disk I/O time:

Indicates the avarage time taken for read  and write operations of this disk.

Secs

The value of this measure is the sum of the values of the Disk service time and Disk queue time measures.

A consistent increase in the value of this measure could indicate a latency in I/O processing.

Disk read rate:

Indicates the number of reads happening on a logical disk per second.

Reads/Sec

A dramatic increase in this value may be indicative of an I/O bottleneck on the server.

Disk write rate:

Indicates the number of writes happening on a local disk per second.

Writes/Sec

A dramatic increase in this value may be indicative of an I/O bottleneck on the server.

Avg queue length:

Indicates the average number of both read and write requests that were queued for the selected disk during the sample interval.

Number

 

Note:

  • For this test to report measures on Unix systems, the sysstat package must be installed on the server (check for the existence of the iostat command on the target system).
  • If the sysstat version installed on the target server is less than 4.0.7, the following measures also will not be available – Data read rate from disk and Data write rate to disk.
  • Detailed diagnosis will not be available for systems operating on AIX platforms.