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iSeries Memory Utilization

Posted on 2016-07-18
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Last Modified: 2016-07-18
I am wondering what the best way is to see how much memory is currently being utilized on an iSeries server.

I have 24 GB of RAM on the server. I am wondering if there is a way to see how much of this is actually being used? Can I see if the system is "RAM-starved"?
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Question by:Matthew Roessner
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by:Dave Ford
ID: 41717629
Start with the WrkSysSts command to show memory-pool sizes and utilization ... as well as disk-space and it's utilization.

HTH,
DaveSlash
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Gary Patterson earned 2000 total points
ID: 41717636
Generally the answer is "all of it", except possibly on some very lightly used systems.  IBM i loads  programs and data into memory as it is called for, and pages out "least recently used" memory pages only when needed to make room for something that an active job is calling for.  The system will generally make use of as much physical memory as you care to install - so if you were to track memory utilization on most non-idle systems, it would go up to 100% pretty quickly after the system is started, and stay there forever.  

As a result, we generally don't use memory % utilization as a meaningful metric on IBM i.

Generally, "RAM starved" systems will show high faulting rates in DSPSYSSTS during peak system utilization periods and will generally exhibit high disk I/O waits if you use a tool like IBM iDoctor Job Watcher.

RAM starved systems usually also tend to have high disk utilization (DSPDSKSTS over 40% busy), and often have lower-than expected CPU utilization peaks, as the system is waiting on date to get paged in off of disk rather than doing useful work.
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