Performance Disk Alarms

This article lists the Performance: Disk alarms of a role, with what each alarm monitors and its factory defaults. Disk performance counters provide the relative health and performance of the disk. The limit and time settings are average benchmarks from disk manufacturers. However, network administrators will better understand the specific needs and requirements on the disks in the enterprise and on individual systems. Thus, the limits and times may need to be adjusted to meet the singular reality of a system and a network enterprise. Both logical and primary drives are evaluated.

The Performance: Disk category is on the Alarms tab of a role (Configure > System Configuration > Roles). To turn these alarms on and change their limits, times, and profiles, see Configure Alarms in a Role.

In the example alarm configuration called out below: If 20% or less of the total usable space on the disk drive is free for a 120 second time period a Yellow level alarm is triggered. If the total usable space is 10% or less for 240 seconds, a Red alarm will be triggered.

Performance Disk Alarms and Defaults

The Default column shows the factory values. A role can change them. To make a disk alarm trigger less often, raise its Yellow Time (s) and Red Time (s).

Alarm	Description	Default
% Disk Time	Monitors the percentage of elapsed time that the selected disk drive was busy servicing read or write requests.	On. Yellow 30 for 120 s, Red 60 for 240 s.
% Disk Free Space	Monitors the percentage of total usable space on the selected logical disk drive that is free.	On. Yellow 20 for 120 s, Red 10 for 240 s.
Disk Queue Length	Monitors the average number of read and write requests that were queued for the disk during the sample interval. A queue length that stays high can mean that the disk cannot keep up with the requests.	On. Yellow 2 for 120 s, Red 2 for 240 s.
Disk Read KB/sec	Monitors the number of bytes per second retrieved from the disk (read).	Off. Yellow 3955200 kB for 120 s, Red 4746240 kB for 240 s.
Disk Read / sec	Monitors the rate (per second) of read operations on the disk. Lower is better.	Off. Yellow 15 for 120 s, Red 15 for 240 s.
% Fragmented I/O	Monitors the rate at which I/O requests to the disk are split into multiple requests. A split I/O may result from requesting data in a size that is too large to fit into a single I/O or that the disk is fragmented on single-disk systems. Disks that have a high % Disk I/O Fragmented may need to be defragmented to improve performance. You may have a high % of Disk I/O Fragmentation and yet the defrag utility tells you the drive does not need to be defragmented. The defrag utility calculates fragmented files across the whole volume. There could be a segment of the volume where frequently accessed files are heavily fragmented and impacting performance. A Solid-State Drive (SSD) may display a high % Fragmented I/O with no performance impact. Lower is better.	On. Yellow 5 for 120 s, Red 8 for 240 s.
Disk Transfer Time (ms)	Monitors the length of time (in milliseconds) for an average disk transfer. This statistic measures the average time of each data transfer, regardless of the number of bytes read or written. It shows the total time of the read or the write. Average Disk sec/Transfer is usually in multiples of the time it takes for one rotation of the disk. Any variation usually represents time for driver processing or time in the queue. For example, on a 7200-RPM disk, the actual Average Disk sec/Transfer would be in multiples of 8 milliseconds. Lower is better.	On. Yellow 250 for 30 s, Red 500 for 30 s.
Disk Write KB/sec	Monitors the number of bytes per second sent to the disk (write).	Off. Yellow 3763200 kB for 120 s, Red 4515840 kB for 240 s.
Disk Write / sec	Monitors the rate (per second) of write operations on the disk. Lower is better.	Off. Yellow 15 for 120 s, Red 15 for 240 s.