HP Sitescope - physical disk %idle time meaning
In my application i am using sitescope for monitoing the performance metrics . I have observed that most of the time , that the idle time % value for physical disk is more than 100% .
Can some please explain what this means.
Also which counters does one use to get accurate assesment for physical disk usage.
The SiteScope Windows Resource monitor retrieves the performance counters provided by Windows. I do not know what causes the disk idle counter to exceed 100%, but there are articles (google) talking about disc utilization abouve 100%. The cuases in these cases were (possibly) parallel requests causing the strange perfromance counters. Additionally there may be impact from caching settings, disk arrays, etc.
To get a clear understanding you'd have to look at specifics for your setup.
Thanks for that bernard.
How does one interpret this value 100% idle time - physical disk . Does this imply that the disk usage is zero
Just to take an example say if the number is 104% does this mean that only 4 % of the disk is being used
as mentioned, the values shown are read from the Windows performance counters and calculated/interpreted by SiteScope. You may want to consult a windows or storage forum to get more details.
Your statement "Just to take an example say if the number is 104% does this mean that only 4 % of the disk is being used" is certainly not correct.
Additionally, it sounds as if you are mixing usage (in terms of GB used / free) and disk utilization (in terms of idle time / bandwidth).
I understand that the HP sitescope tool uses -> windows perfmon to get the numbers for the counters being monitred.
As per the perfmon definition
% Idle Time
This counter provides a very precise measurement of how much time the disk remained in idle state, meaning all the requests from the operating system to the disk have been completed and there is zero pending requests.
This is how it’s calculated, the system timestamps an event when the disk goes idle, then timestamps another event when the disk receives a new request. At the end of the capture interval, we calculate the percentage of the time spent in idle. This counter ranges from 100 (meaning always Idle) to 0 (meaning always busy).
Which brings me back to my original question -> So assuming we have a standalone machine ( not a raid ) , then if we we 100% as the reading it would be safe to conclude that the disk has been idle for most time. Is that correct ?
% Disk Time may exceed 100 percent in the Performance Monitor MMC
This behavior can occur because some controllers allow the operating system to use overlapping input/output operations for multiple outstanding requests. The disk performance counters time the responses by using a 100 nanosecond precision counter, and then report the cumulative statistics for a given sample time. This sample time could go over 100 percent if, for example, you have 10 requests that completed in 2 milliseconds each in a 10 millisecond sampling interval. If you have multiple disks in a Raid arrangement, the overlapped input/output happens because the operating system can read and write to multiple disks, and this could show values that are higher than 100 percent for this counter.