Comments on: Optimizing Memory Utilization

By: Active memory and configured memory « Designing vSphere

Active memory and configured memory « Designing vSphere — Tue, 09 Mar 2010 16:33:41 +0000

[...] Why is it important to track active memory –check this post [...]

By: The Truth About Hyper-V Memory Overcommit : BizzRoot – Splash News

The Truth About Hyper-V Memory Overcommit : BizzRoot – Splash News — Fri, 29 Jan 2010 19:30:12 +0000

[...] The Cost Per Application Calculator makes it clear that investing in VMware vSphere 4 significantly reduces your datacenter hardware footprint and associated costs. Scott Drummonds, the VMware performance expert, recently explained how memory overcommit is the only way to effectively use all of the physical RAM in a hypervisor. [...]

By: Microsoft failed to implement memory overcommit in Hyper-V R2 | VCritical

Microsoft failed to implement memory overcommit in Hyper-V R2 | VCritical — Wed, 13 Jan 2010 13:21:21 +0000

By: Scott

Scott — Mon, 11 Jan 2010 17:11:49 +0000

There is no number that is “true in all cases”. As I say in the article, “A virtual machine’s active memory is dictated by the application and its usage”. So, the active memory will change from VM to VM, from system to system and DC to DC. 25% is an arbitrary selection, probably near average.

Scott

By: techstarts

techstarts — Mon, 11 Jan 2010 16:06:49 +0000

Hello Scott,
Is 25% active memory true in all cases ? If so then design which i proposed here will be totally void…http://vcp4.wordpress.com/2010/01/08/one-min-design-guide-of-40-2gb-vms/

By: VMware ESX Memory Over-commit «

VMware ESX Memory Over-commit « — Fri, 08 Jan 2010 04:11:37 +0000

[...] http://vpivot.com/2010/01/06/optimizing-memory-utilization/ [...]

By: Scott

Scott — Fri, 08 Jan 2010 01:57:35 +0000

Wow. Fantastic numbers!

By: Fernando

Fernando — Fri, 08 Jan 2010 01:38:56 +0000

But TPS normally gives excellent results, since we tend to have too many identical OSes (even if the applications differ). I just posted this on Gabe’s blog, will paste again:

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Some real data, from a customer cluster, in full production. I looked at 4 hosts from 10 available:

Host 1 – 16 VMs – 12GB Shared – 30 GB Used – 64GB Total
Host 2 – 14 VMs – 11GB Shared – 30 GB Used – 64GB Total
Host 3 – 15 VMs – 10GB Shared – 32 GB Used – 64GB Total
Host 4 – 25 VMs – 30GB Shared – 32 GB Used – 64GB Total

Yes, I have a host right now, with 30GB Shared (I looked many times, and confirmed with the performance data on vCenter to be sure).

These are 99% Windows Server 2003 VMs, which explains the huge amount of page sharing.

Hosts are still with too much available memory, but would probably be near the limits without TPS. Also, MEMCTL is zero on all cases, ballooning did not even kicked in. I can *easily* double the VM density on this situation, since the memctl driver would save even more memory.
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By: Scott

Scott — Thu, 07 Jan 2010 00:10:02 +0000

TPS makes some of the calculations I provided a little more complex. The amount of active memory would decrease some, as would the inactive memory, which is immaterial to the calculation. The value of TPS is also workload-dependent, making it even more difficult to apply to a hypothetical calculation. TPS can only help this calculation, but by how much I have no way of knowing. So I eliminated it for the sake of simplicity.

By: Duncan

Duncan — Wed, 06 Jan 2010 23:13:21 +0000

Wouldn’t TPS make a difference? Active pages will also bw deduped. So although 25% is active ESX might store way less..