Windows Server 2008 Cached Memory

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Hello experts,

I've got what seems to be a cache memory problem with my Server 2008 machine.  The machine has two quad core Xeon processors and 24GB of memory.  The problem is that the server seems to cache an awful lot of memory, making the server very slow and unresponsive.  I've been all over the internet looking for a solution...hopefully someone can help!  I've attached a screen of Task Manager with the cache amount highlighted.  

The server's main job is Hyper-V.  There are 4 virtual machines on this server.  Each virt has 4GB memory and one of the processor cores allocated to it.  This should leave 8GB memory and four cores for the host OS.  The server also has a small file share located on it.  That share is less than 75GB and is not accessed that often.  As I said, the main problem is the slow response of the host OS.  To manage Hyper-V, we have the System Center Virtual Machine Manager console installed.  Sometimes it can take, no joke, 5 minutes for the console to open.  Very frustrating.

Thanks!
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Commented:
Make sure you are using synthetic drivers on your vms and not emulated. Go into hyper-v manager and look at your network cards. Also make sure you have SP2 for 2008 applied and have your vms using the latest version of the integration tools.

you have 16 GB of memory  on your host server correct?

Commented:
Emulated drivers use more resources on the host machine than synthetic drivers.

Author

Commented:
Hi plimpias,

Thanks for the replies!  The server is already updated to SP2, and the drivers are indeed emulated.  Forgive the question, but I'm not sure how to change those to synthetic...there are four VM's connecting to a network then finally going through the network card.  

The server has a total of 24GB memory.  16GB is for the virtual servers and 8GB is left for the host.

Thanks again!
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Commented:
Open up VMM manager and look at the properties on the VM
Go the the hardware configuration tab
under network adapters look on the top and see if it is emulated.
If it is you will need to remove it and from the VM and add a new nic, this time choosing synthetic.

Author

Commented:
OK, I will start changing the adapters tonight as the users drop off (three of the virts are terminal servers) and see what happens.  I'll keep you posted.

Thanks again!

Commented:
I am not sure why cause this happened ( high memory cache maybe caused heavry I/O traffic). you can try following suggestions:
1. In SCVMM admin console, reserve 8GB memory for host (default is 2GB).
2. Download and install the last update for hyper-v from Microsoft website.
3. Review hyper-v host system and application events to verify what's wrong in the system.
Hope this helpful.

Commented:
He already said the 8 GB is left for the host and he is on the latest version of hyper-v with SP2.

Author

Commented:
Well, I changed the network drivers to synthetic and rebooted, but no change.  The server is still dumping all available memory into cache leaving none free.  I went through all the logs of the server and nothing indicates any issues.

A very annoying issue indeed.  Any other ideas would be greatly appreciated!

Thanks!

Commented:
Hi,
What version do you have running, core or full installation?
Besides Hyper-v and the file server role. What other programs are installed on this host? What i would recommend doing is disabling all non microsoft startups and see if the issue still persists. If it does we need to run perfmon to determine what the problem is.

Also a may help while having the task manager open go to processing, the in view choose colums and add all the memory options.

Author

Commented:
Hi plimpias,

It's the full installation.  The only other program installed on this server besides hyper-v and the file shares is the System Center Virtual Machine Management Console, which does require a bunch of overhead since a SQL engine is required to catalog the VM's.  But that SQL engine is an MSDE version, I think (SQL Express?).

I will examine task manager as well as check the startup services to see what can be done.  I'll report back on any findings.

Thanks again for all your help!

Commented:
What I would do is disable vmm And SQL and see if it changes the memory. I think that may be the issue

Author

Commented:
OK...but wouldn't that defeat the purpose of VMM?  

Commented:
Yes of course bit this is just to see if the memory problem goes away. It is recommended that you run hyper on server core edition by itself. Other service on the host have a big affect on the performance

Author

Commented:
OK, I'll give it a try and report back the results....

Author

Commented:
I disabled the VMM console as well as the SQL engine, and, as you would probably expect, performance jumped up pretty drastically.  The question becomes, is there a known issue with VMM and SQL in Hyper-V?  I can manage the VM's with the Hyper-V role in Server 08, but that really isn't the way I would like to do this, since I need physical-to-virtual conversions and the ability to store the virtual machines.  Not to mention the licensing fees I've already paid....

Any other help you can give would be greatly appreciated.

Thanks!
Commented:
SQL is pretty resource intensive, it is always recommended that you have a seperate box for the management on the hyper-v solution. I would recommend that you remove everythinn from the physical box of the Hyper-V server except for the hyper-v role.

Author

Commented:
Hmmmmm....the question now is where do I put it...but that's a problem for me!

I'll check into a new box for the console and SQL, but it appears our problem has been found.  Again, for anyone else, plimpias' suggestion of removing VMM and SQL resulted in a large performance gain on our server.  We will be looking to move our VMM and SQL from the server to another machine.

Thanks plimpias!

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