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I am trying to setup perfmon on a Windows 2008 R2 server to monitor memory usage on a server for 1 week. I have never used perfmon before, but some basic tutorials explained how to pick between different performance counters and get the basic application up and running, thereby generating reports.

I was looking for something similar to "Physical Memory" (which can be found in Task Manager >> Performance tab) which displays memory usage data as a percentage between 0% and 100%. I do not really care about the units of the counter, but I would like something that gets me a similar metric to the Performance tab.

When I tested using Memory\%Committed Bytes in Use, that counter does not seem to be giving me what I want; it seems to be measuring something else. On my specific server, I have 8GB of RAM. Using the Task Manager, I could see that the server was using 1.5GB of RAM, but when I ran the performance counter test, the %Committed Bytes was shown as having a value of 11, with a scale of 1.0--which I assume translates to 11%. Task Manager was reporting 19% over that same time interval, so I do not know what to make of that discrepancy.

Perhaps the Available MBytes is the correct metric (with a reporting scale set to 0.001) for my needs, and the results I got in testing say 6.618GB, which looks correct (this requires changing the graph type to "Report"--I guess since this only provides a single value as a result, 6.618GB must be the average over the entire time interval the performance counters are running?).

Are either of these performance counters appropriate to use for my purposes? What is the best way to display the data I am trying to observe over an entire week? I really would like to see the highs and lows of memory usage over a week time period.

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1 Answer 1

up vote 3 down vote accepted

Monitoring Available MB is sort of useless. No one cares how much RAM is free, the OS should be consuming a large amount of "free" RAM for buffers/cache. That's where Committed Bytes come in. That's memory that's actually in use. Anything else in memory is just there for caching and will be released if a program actually needs that memory.

% Committed Bytes is what you should care about, since it's a meaningful measurement. If you just want something that mirrors task manager, then sure, go for Available MB but don't expect it to mean a whole lot.

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Thank you. That is a very important revelation about which counter to use. Since % Committed Bytes is the correct counter for what I really want, how should I interpret the graph information related to that counter? I assume using the Line Graph reporting format and having a scale of 1.0 leaves me with about 11% of memory usage, as I indicated above. If I do "Report" as my format, I just receive a single number of 10.368. –  nairware Feb 11 '13 at 15:43
    
The 10.368 is likely the average over the entire collection. You've interpreted the units correctly. At a scale on 1.0, a mark at 11 on the graph corresponds to 11% of memory being committed. –  MDMarra Feb 11 '13 at 15:48

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