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I know what the disk io, disk queue length and other measures are, but what does 'Highest active time' mean?
Is it the amount of time it is busy handling requests, or something else?
When it is high, does it mean the CPU is busy doing some IO work, or is it just indicating that the disk is busy handling requests?
I'm trying to work out if 50% active time means that 50% of the time the disk is either seeking, reading or writing, rather than the kernel is spending 50% of it's time servicing IO requests.
Edit Another quick data point here. If you look at the difference between an SSD and a physical disk, the SSD has significantly less activity, so I guess this really means the amount of time the operating system is waiting for the disk to respond and returning data.
@TomTom Perhaps you could add an answer to clarify. I understand your point in a RAID, but the metric would seem to at least correlate strongly with poor performance, similar to what's described here. Idling your taxi does waste cash (engery.gov ppt).
– ruffin – 2014-12-02T14:13:24.667Not totally. The problem is that I can keep a Hard disc active without a lot of activity. So, 100% active does not necessarily mean "delivering me all the data it can". – TomTom – 2014-12-02T14:22:05.737
@TomTom and DanO : hello, I've question. In my case my TFS build server is not using RAID but a single hard drive. The disk highest active time when active is mostly above 80%, often hit 100%. Is this a bottleneck? Are upgrading my hard-drive (SSD or dedicated hard-drive per build agent) will help? I don't have physical access to the machine right now because I need to propose it first to my manager. Thank you. – hendryanw – 2015-03-31T09:39:36.283
Commone sense tells you that something hitting 100% utilization is bottlnecked there. Any experience wiill tell you builds are IO intensive. Get an SSD - you will be surprised. – TomTom – 2015-03-31T18:45:12.330
I'm getting figures of up to 13,000 on a currently-busy server!
I'm thinking I'll go with % idle time (currently 0.05) – Michael – 2015-11-12T04:47:57.370
I think that rather than being the _Total it is the MAX of the individual drive statistics. Of course this would be the same thing if there is only one disk. If you look under the 'Storage' section of the disk tab you will see the 'Active Time (%)' column the 'Highest Active Time' is the MAX of this column. – Martin Brown – 2012-01-24T13:12:52.010
As a note - it is a totally usless statistics. Because "busy" is not "overloaded". Especially on servers with multi disc RAID subsystems that are capable of significant throughput and with a ton of separate IO streams the disc subsystem is pretty much always having SOME command in processing, just not relly anything that keeps it busy. THat is like measuring a taxi utilization by the time the engine runs - but it may only run on a parking place to keep the heating going in winter. I always measure Seconds/IO, which is a GOOD indication - when it grows, the disc subsystem is overloaded. – TomTom – 2012-05-30T09:16:04.837