2.2.3 Example of monitoring the disk

By monitoring the disk, you can detect a shortage of disk resources and identify a bottleneck caused by the disk. If you monitor the disk continuously, you can also identify trends in increasing disk usage, which can help you determine the system configuration and the timing of expansion.

Organization of this subsection

(1) Overview of disk monitoring
(2) Example of a monitoring template for monitoring the disk

(1) Overview of disk monitoring

The disk stores programs and the data used by the programs. If a shortage of free space occurs on the disk, not only does the system's response become slower but problems such as data loss also occur. A shortage of free disk space might also lead to other types of performance deterioration, such as a reduction in process response speed.

If there is not enough free disk space, a response wait status might occur when programs input data from the disk and output data to the disk. If the disk is suspected of being responsible for a bottleneck, such as because of a shortage of free disk space, first check if the disk has become fragmented. Next, check if an unreasonably large amount of disk space is being used by invalid files and if sufficient free space has been allocated.

The following table lists and describes the records and fields that are used for monitoring the disk.

Table 2‒7: Records and fields used for disk monitoring
No.	Record	Field to be used	Description of value	Interpretation of value
1	`PI_PDSK`	Busy %	Disk busy rate	When the threshold value is exceeded continuously, there might be a concentration of processing that uses the disk.
2		Avg Disk Time	Average disk I/O operation time	When the threshold value is exceeded continuously, there might be a concentration of processing that uses the disk.
3		Total MBytes/sec	Number of bytes transferred between disks (per second)	When this value is high, the system is considered to be running efficiently.
4	`PI_LDSK`	Free Mbytes %	Free disk space percentage	When this value is low, there might be a shortage of disk capacity.
5	`PI_LDSK`	Free Mbytes	Free disk space	When this value is low, there might be a shortage of disk capacity.

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(2) Example of a monitoring template for monitoring the disk

This subsection describes examples of alarms and reports that are provided as a monitoring template for monitoring the disk.

PFM - RM for Platform provides alarms and reports, such as the Disk Busy % alarm and the Avg Disk Time Status report. To obtain more detailed performance of the disk, you must monitor various aspects of the disk.

(a) Alarms

The following table lists and describes the disk-related alarms.

Table 2‒8: Examples of alarms related to disk monitoring
No.	Alarm	Record	Field	Abnormal condition	Warning condition	Interpretation of value
1	Disk Busy %	`PI_PDSK`	ID	<> _Total	<> _Total	A disk busy rate of 80% or higher is treated as the warning or abnormal status. When this value becomes greater than the threshold value set in the warning or abnormal condition, disk access might be busy.
2	Disk Busy %	`PI_PDSK`	Busy %	>= 90	>= 80
3	Disk Service Time	`PI_PDSK`	Avg Disk Time	> 0.1	> 0.06	An average disk I/O operation that exceeds 0.06 second is treated as the warning or abnormal status. When this value becomes greater than the threshold value set in the warning or abnormal condition, a very large I/O operation might have occurred.
4	Disk Space	`PI_LDSK`	Free Mbytes %	< 5	< 15	A free disk space percentage rate that is less than 15% is treated as the warning or abnormal status. When this value becomes less than the threshold value set in the warning or abnormal condition, a shortage of free disk space might have occurred. You need to take an appropriate action, such as deleting unneeded files, compressing files, optimizing the disk, or expanding the disk.
5	I/O Wait Time	`PI`	Wait %	> 80	> 60	A disk I/O wait time that exceeds 60% is treated as the warning or abnormal status. When this value becomes greater than the threshold value set in the warning or abnormal condition, a delay in I/O operations might have occurred, such as a delay in database update processing.
6	Disk Free Size	`PI_LDSK`	ID	<> _Total	<> _Total	Unused disk space of less than 10,240 megabytes is treated as the warning or abnormal status. When this value becomes less than the threshold value set in the warning or abnormal condition, a shortage of unused disk space might have occurred. You need to take an appropriate action, such as deleting unneeded files, compressing files, optimizing the disk, or expanding the disk.
7	Disk Free Size	`PI_LDSK`	Free Mbytes	< 5120	< 10240

(b) Reports

The following table lists and describes the disk-related reports.

Table 2‒9: Examples of reports related to disk monitoring
No.	Report name	Information displayed in the report
1	`Avg` `Disk` `Time` `Status`	Displays the average I/O operation time for the physical disk.
2	`Free` `Megabytes` `-` `Logical` `Disk`	Displays information about the logical disk space being used.
3	`Physical` `Disk` `Busy` `Status`	Displays the percentage of time during which the disk was busy.

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