Why does memory utilization show negative results? RRS feed

  • Question

  • Hi there, can someone help to explain to me why and what is the meaning when MAP reports a server with negative results?

         Machine Name       |   CPU Utilization   |   Memory Utilization   |         3.00            |         -1.122.03

    All other servers are fine except this one...

    Ray Chou | MVP SCOM |
    Wednesday, August 4, 2010 2:32 AM

All replies

  • I'm assuming that this is from the ServerVirtRecommendation-<date>.xlsx Excel spreadsheet?  The UtilizationBeforeVirtualization tab in particular?  Assuming so, here is a potential explanation.  MAP uses the formula:

    Memory Utilization MB = (Total MB RAM) - (Average available MB RAM)

    to determine memory utilization.  However, the sources of data for Total MB RAM (WMI) and Average available MB RAM (performance counters) are different and if the data for Total MB RAM wasn't retrieved for some reason or reported an incorrect value (say 0), then you could end up with a negative number for memory utilization given the above formula.

    Investigating further would require running some SQL queries against the DB that exhibits this problem.

    Wednesday, August 4, 2010 7:23 PM
  • Hi,

    Can i just take   -1.122.03 , to come out with memory utilization. For example, i got 5GB total MB RAM.

    so Memory utilization = 5GB -  1.122.03

    = 3998.

    laiys | My
    Friday, August 6, 2010 1:27 AM
  • I just took a look at a sample PerfMetricsResults-<data>.xlsx report and you should be able to determine if this is correct from that Excel report.  In particular look at the MemoryUtilization worksheet in that report for the server that is reporting negative memory utilization.  There are two columns "Total Memory (MB)" and "Available Bytes (MB)" that correspond to what is used in the calculation:

    Memory Utilization MB = (Total MB RAM) - (Average available MB RAM)

    If "Total Memory (MB)" is zero or less than 5GB, then what you suggest above is reasonable.  If "Total Memory (MB)" is 5 GB, but "Available Bytes (MB)" is greater than 5 GB, then "Available Bytes (MB)" is definitely being reported incorrectly and this calculation won't work.  In that case you might want to assume 4.5-5 GB of memory usage for that server to be conservative.

    Friday, August 6, 2010 5:54 PM