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 physical disk on the 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. use sudo –This parameter is of significance to Linux and Solaris platforms only. By default, the USE SUDO parameter is set to No. This indicates that, by default, this test will report the detailed diagnosis for the Disk busy measure of each disk partition being monitored by executing the /usr/bin/iotop command or /usr/sbin/iotop command. However, in some highly secure environments, the eG agent install user may not have the permissions to execute this command directly. In such cases, do the following:

    • Edit the sudoers file on the target host and append an entry of the following format to it:

      <eG_agent_install_user> ALL=(ALL) NOPASSWD:<Command_with_path>

      For instance, if the eG agent install user is eguser, then the entries in the sudoers file should be:

      eguser ALL=(ALL) NOPASSWD: /usr/bin/iotop

      eguser ALL=(ALL) NOPASSWD: /usr/sbin/iotop

    • Finally, save the file.
    • Then, when configuring the test using the eG admin interface, set the use sudo parameter to Yes. This will enable the eG agent to execute the sudo /usr/bin/iotop command or sudo /usr/sbin/iotop  and retrieve the detailed diagnosis of the Disk busy measure.
  6. DETAILED DIAGNOSIS – To make diagnosis more efficient and accurate, the eG Enterprise suite embeds an optional detailed diagnostic capability. With this capability, the eG agents can be configured to run detailed, more elaborate tests as and when specific problems are detected. To enable the detailed diagnosis capability of this test for a particular server, choose the On option. To disable the capability, click on the Off option.

    The option to selectively enable/disable the detailed diagnosis capability will be available only if the following conditions are fulfilled:

    • The eG manager license should allow the detailed diagnosis capability
    • Both the normal and abnormal frequencies configured for the detailed diagnosis measures should not be 0.
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.

Disk read time:

Indicates the average time in seconds of a read of data from the disk.

Secs

 

Disk write time:

Indicates the average time in seconds of a write of data from the disk.

Secs

 

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

 

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.

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.

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.

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.

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.
  • The eG agent monitoring Solaris hosts can only measure the time for access to the disk (not differentiating between read and write times). This is why, this test reports the Disk read time and Disk write time to be the disk access time reported by the operating system