Can we overcommit double the amount of physical memory

[ab_lal]

The vSphere 4 Advanced memory management mention about RAM over-commitment. Increase memory utilization by configuring virtual machine memory that safely exceeds the physical server memory. For example, the sum of the memory of all virtual machines running on a server with 8GB physical memory can be 16GB.

If we overcommit double the amount of physical memory, Will all the VM's run effectively withour raining errors?

[a_p_ · Accepted solution]

It really depends on how much memory your systems really need. You can overcommit as much as you want, however as soon as the VM's consume more RAM than physically available, ESX needs to swap and at this point performance degrades.

André

[ab_lal]

Thanks André

Thats what i believed, so its better to keep track of the amount of Physical memory you have committed and keep it at 90 to 95 %

Cheers

[a_p_]

Not really. Overcommitting memory is really useful.

Consider systems with variable workloads. They may temporarily need more RAM for calculations or other processes, but usually run with less memory. Therefore you should look at the average memory usage of the systems and give them enough RAM to handle peaks.

However memory is not that expensive anymore, so having enough physical memory is always the best bet.

I remember the times where bought memory because the price went down to ~100$ per MB (yes MB, not GB for the younger audience in this forum )

André

[golddiggie]

I would keep track of how much memory the host is actually using, rather than what you've committed to VM's... I have 16GB of RAM inside my lab host, with 17.5GB committed/allocated to VM's. Of that, I'm using about 12.5GB right now (ranges from about 10GB-14GB used)... I could add a couple of additional VM's, depending on what they do/run, before adding more physical RAM to the host (or another host to share the load)...

I would enable email alerts for when you're using more than 90% of the hosts RAM, so that you don't run into troubles... If you're using a vCenter Server, then you get the ability to have the alarms (not present in the host only vSphere Client)... The ability to monitor things in this fashion is just another reason why it's a good idea to have vCenter Server in place... You might be able to do the same function with vFoglight Qucik View... I'm planning on testing the product shortly, just haven't had time to get to it yet...

VMware VCP4

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