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how to calculate physical servers needed for an openstack project

asked 2014-03-15 13:16:04 -0500

black sensei gravatar image

Hello I would like to try to calculate the number of physical servers needed to host 100 Virtual machines of 4GB RAM each a quad-core at 2.2Ghz and 40GB of HDD. Let's say I have a 2 types of servers I can have either

2x AMD Opteron 6272, 32 Cores (2x16)
2x 2,000 GB SATA II HDD


2x Intel Xeon E5-2420, 12 Cores (2x6)
2x 2,000 GB SATA II HDD

what is the formula to come up with the total physical servers needed for the project.

I have a little doubt in my understand of how the whole system would work out so in a system like mine where there are physical servers available to host all of the 100, how are backups of the instances catered for?

Thanks for helping

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answered 2014-03-18 19:06:40 -0500

You can do the math in your head, you need 100 x 4GB of memory, I would add a bit more to be conservative. You need 100 x 4 vCPU (depends on how much you over subscribe them 16:1 is the default, I would suggest 6:1) and you need 100 x 40G of disk.

400GB of Memory 400 vCPU 4000 GB of Disk or 4TB

3 servers with 128 GB of Ram, Dual 8 Core CPU, 4 x 1TB drives would give you 512GB of Ram, 576 vCPU (using 6:1 and assuming Intel Hyperthreading is yes) and 12TB of disk.

You can take this same formula and apply it to the servers you listed above.

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answered 2014-03-16 16:44:43 -0500

diegolopez gravatar image

look at this: ( (

Hope it helps

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Asked: 2014-03-15 13:16:04 -0500

Seen: 1,146 times

Last updated: Mar 18 '14