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Questions on vmware and virtualization

Posted on 2013-01-14
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Last Modified: 2013-01-15
Hi all ,

one of my customers has these two questions and not sure what the best answer is. Any ideas would be appreciated


Please advise what limits there are in amounts of physical memory we can have in a virtual server.  ( so for example if i have a physical host with 23 GB RAM) how much ram can i allocate to the virtual machines ? Can i create vms and allocate 32 GB of ram on these vms ?
 
In addition if we want the equavalent of 2 Quad Core CPU's does that mean we need to request 8 CPU's? Is that an option?
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Question by:c_hockland
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by:Stelian Stan
ID: 38776910
If you have a host with 23 GB of RAM that means that's the maximum amount of memory you have for your VM's.

If you have two quad cores that means that you have 8 virtual available for your VM's.
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Stelian Stan earned 2000 total points
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by:c_hockland
ID: 38776992
many thanks !
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by:aleghart
ID: 38777695
You can overprovision RAM, hard drive space, and CPU.  If your VMs are running at 2% CPU, 25% RAM, and 25% hard drive space...with no growth projected, and no heavy simultaneous loads.

In an ideal world, you'd be using virtualization to maximize the utilization of the hardware.  If you have 8 Server 2008 boxes at 4GB RAM each, they might only be using 1GB of RAM.

Running out of RAM will cause the host to swap, and the VMs should fare fine.  If the VM guest is provisioned with 2GB and runs out of RAM, the guest will spool.  The host will only see excessive amounts of storage and CPU activity.

Four cores of CPU is a lot.  Have you tried with one first, and monitor the guest & host?  You may be surprised how little CPU provisioning you need.  1 or 2 cores can still run a database, instead of 4 or 8 from the start.

If your host has 24GB of physical RAM, then your guests (in aggregate) can only use that much physical memory before the host will start to swap.  This doesn't limit you to creating only 24GB of VMs.  Each VM can have a different location for swap.  Default is swap stored with the VMDK.  You can move this to a host local drive, local RAID, faster SAN, or local SSD.

I have a Server 2008 VM idling for a dev project that's using less than 1% of its 4GB RAM, and 0% of it's CPU.  Another that's currently replicating a small database is using between 1-10% of the CPU and less than 5% of its 2GB RAM.
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