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milesmeridith
Enthusiast
Enthusiast

Determining how many VM's my two VSphere host can support

I have two  HP Proliant DL320 G6 servers running VSphere 5.1. I want to know how many servers I can expect to support. Below are the specs. I know this greatly depends on what the hardware requirements of the VM I am going to be running, however if I can get an idea.

2 HP Proliant DL320 G6 each with the following specs

Intel Xeon E5504 2.0 GHZ 4 Core Proc

1 TB Raid 1+0

96 GB RAM

HP Smart Array P212 controller

Basically I want to know if I should be more concerned with Processor or Memory. Is my calculation correct that all VM's would have to share 8 GHz, and VSphere will be able to distrubute the proccessing power to the different VM's when they need it?

Ive read some of the posts on this and most seemed to be focused on memory usage. But with 192GB total of ram I think I should be more concerned with Processor power no?

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sparrowangelste
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generally it is the memory that is the bottlneck.

having only 1cpu with 4 cores thogh cpu might be your bottle neck here.

--------------------- Sparrowangelstechnology : Vmware lover http://sparrowangelstechnology.blogspot.com
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a_p_
Leadership
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While it is relatively easy to calculate the memory requirements, it's not as easy to estimate the CPU usage. Your CPU has 4 cores but unfortunately no HyperThreading, so the VM's will have to share 4 cores which are scheduled to the VM's (not parts of the 8 MHz). What may limit the performance are the 2 disks and probably the RAID controller. It's not the capacity of the disk that's most important, it's the IOPS and with only 2 disks (I assume you are using the 7200 RPM disk) you will be limited in the number of VM's you can run with good performance. In addition to the disks you need to ensure the P212 is equipped with BBWC, this makes a HUGE difference in disk performance too.


André

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milesmeridith
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Thank you for the feedback. Can you please elaborate what this means? "Your CPU has 4 cores but unfortunately no HyperThreading, so the VM's will have to share 4 cores which are scheduled to the VM's (not parts of the 8 MHz)."

I think I was mistaken in what I said. Since there are two hosts and each one has 2.0 GHz with 4 cores that would equal 16 MHz no?

Each host has 2 1TB drives. I looked up the specs but I saw no info on IOPS. It is 7200 RPM.

http://h30094.www3.hp.com/product.asp?sku=10311140&mfg_part=625609%2DB21&pagemode=ca

I don't believe my P212 has BBWC since it said it was part of an upgrade when I researched.

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a_p_
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Since there are two hosts and each one has 2.0 GHz with 4 cores that would equal 16 MHz no?

That's correct, the cores sum up to 16 GHz. However, each host can only use its own resources, that's why I was talking about a single host.

The CPU scheduler can only schedule "complete" cores (vCPUs) to a VM, not parts of them (e.g. 1.5 MHz to one VM and the other 0.5 MHz to another VM simultaneously). This means that the more VMs are powered on, the more have to "share" a single core.

André

PS: Maybe interesting for you to read: http://www.vmware.com/files/pdf/techpaper/VMW_vSphere41_cpu_schedule_ESX.pdf

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milesmeridith
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Thank you I think I understand better now. Just to be clear. If I have one HP with 8 VM's each utilizing one core, I couldn't create another machine? Right now I have 6 VM's running on one HP that I migrated over from Hyper-V and if I check settings they either say 1 or 2 cores. I guess my second question is can I over commit CPU usage on each host?

And then if so what are the implications if I have to power off one of my two hosts? Will VMotion keep them up and running on the other host?

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sparrowangelste
Virtuoso
Virtuoso

milesmeridith wrote:

Thank you I think I understand better now. Just to be clear. If I have one HP with 8 VM's each utilizing one core, I couldn't create another machine? Right now I have 6 VM's running on one HP that I migrated over from Hyper-V and if I check settings they either say 1 or 2 cores. I guess my second question is can I over commit CPU usage on each host?

And then if so what are the implications if I have to power off one of my two hosts? Will VMotion keep them up and running on the other host?

you can use more than 8, 25 vms on 1 core can be possible, you can definitly overcommit.

but then you will have a high ready time on the vms where they will wait for cpu.

so as long as your vms are not cpu intensive you are ok.

--------------------- Sparrowangelstechnology : Vmware lover http://sparrowangelstechnology.blogspot.com
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