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Windows Server 2008 R2 consuming all available RAM for CACHE

Posted on 2013-01-06
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Last Modified: 2013-01-07
I am running a windows server 2008 R2 standard as a host for 6 virtual machines. The server has 2 x quad core XEONS and 32GB of Ram.

After I restart the host, I can boot all the virtual machines boot and consume the expected amount of RAM and for a few hours cache RAM remains low when viewed from TASK Manager. If I log in 6 to 10 hours after the host is restarted and all VM's are running, the HOST has consumed all remaining RAM (as much as 12GB) into CACHE and leaving ZERO FREE memory.

At first I thought this might be a Backup Program I was running, so I uninstalled it, and other than the base services for the HOST, I have no other applications running on the HOST. I have no idea why the server is consuming ram and I'm not sure if this is or can be affecting the performance of the VM's. Any thoughts on how to manage the CACHE memory or even how to clear it would be appreciated.
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Question by:erocon
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by:erocon
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Update, I installed Microsoft Security Essentials a ran a virus scan to see if it was a bug, the scan came back clean. Attached is an image of the results of RAMMAP: the memory being consumed is in MAPPED FILE

RAMMAP File Upload
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by:gt2847c
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Cache memory is not necessarily/technically consumed memory.  It can be allocated to processes requesting memory.  If you want to see how much memory is actually available to processes, start the resource monitor (Start->Programs->Accessories->System Tools->Resource Monitor or also available as a button on the Performance tab of the Task Manager) and select the Memory tab.  At the bottom of the Memory Tab, you'll see a graph of total memory.  

Hardware Reserved - video memory, BIOS, HW resources, etc
In Use - claimed by OS or processes
Modified - memory that has data that would have to be flushed to disk before released for swapping
Standby - memory released but still linked to processes, can be reallocated to processes
Free - not yet allocated memory


The "Available" entry at the bottom of the graph is essentially what the OS can provide to requesting processes.

Here's an article that provides a lot more details
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by:erocon
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Update: I have removed 12 GB of RAM since that was the lat thing I did before I noticed this problem. I am now running 24GB ram
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by:erocon
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Thanks gt2847c:
Attached is a copy of the resource monitor stats: Based on what you are saying, the "10891 MB Available" which includes 777MB of FREE ram is actually available for other processes and services, so then I should not be concerned about performance issues like Network connections or disk writes. I will read the article.

 

Thank you.
ResourceMonitor.jpg
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gt2847c earned 500 total points
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The performance on the VMs can be affected by many things.  Watching the resource monitor will help you identify things that may be impacting performance like disk access and such.  If you notice performance dropping on the VMs, bring up the resource monitor on the host and see if you see limiting events...  Things to watch for are:

Memory tab - Hard Faults/sec and Commit Charge.  These will go high when you run into memory contention (need more RAM on the system)

Disk tab - Queue Length.  This is how many things are waiting disk IO.  If this number gets high, your system is IO constrained on storage.  If this is a production system with performance requirements, you may have to rearrange VMs, storage setup and such to lower the queue length.  Adding another storage array, moving VM images to other disks, etc. can help lower IO contention and improve performance.

Network - Interface utilization.  You need to make sure you're not over-committing your network interface for your VMs.  Too much contention here will cause performance issues.  If you have high utilization on a given NIC, consider adding another NIC and rearranging your VMs to spread the load around.

VM systems generally require tuning to make sure you're providing good performance.  Keeping an eye on the trending of the various subsystems on your host machine can help you prevent getting surprised by performance issues...
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