Disk Activity Test
On Linux systems, the test will return the input/output utilization of each "device" on the system. The device name is in the format "hdiskn" for 2.2 kernels, where "n" is the device number. For newer Linux kernels though, the device name is displayed as "devm-n", where m is the major number of the device, and n a distinctive number.
Target of the test : Any host system
Agent deploying the test : An internal agent
Outputs of the test : One set of results for each host monitored
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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. The detailed diagnosis of this measure will reveal the top-10 I/O-intensive processes executing on the host. |
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 |
|
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 response time |
Indicates the average 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 |
|
Avg IO read size |
Indicates the average number of bytes transferred from disk during read operations. |
KB |
Larger I/Os tend to have higher latency (for example, BACKUP/RESTORE operations issue 1 MB transfers by default). |
Avg IO write size |
Indicates the average number of bytes transferred into disk during write operations. |
KB |
|
Split IO |
Reports the rate at which the operating system divides I/O requests to the disk into multiple requests. |
Splits/Sec |
A split I/O request might occur if the program requests data in a size that is too large to fit into a single request or if the disk is fragmented. Factors that influence the size of an I/O request can include application design, the file system, or drivers. A high rate of split I/O might not, in itself, represent a problem. However, on single-disk systems, a high rate for this counter tends to indicate disk fragmentation. This measure is reported for Windows VMs only. |
Avg IO read size |
Indicates the average number of both read and write requests that were queued for the selected disk during the sample interval. |
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Avg IO write size |
Indicates the average number of both read and write requests that were queued for the selected disk during the sample interval. |
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Split IO |
Indicates the average number of both read and write requests that were queued for the selected disk during the sample interval. |
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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).
- For this test to report measures on Linux systems in particular, the iotop command should exist on the 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.