Best hardware to host multiple vm's?

[Meatbeast]

Hi,
I need to build a host that will hold 10 + vm's however only 2 or 3 at the most will be used at one time, unfortunately budget isn't great.... the guests will be server 2012 or server 2008 but the one app they run, isnt too intensive.

so should I buy something like this,

ebay item 141991362452 dell power edge 6850 with 4x dual core xenons and put 64gb or ram in it?

or would this be better,

ebay item 172281165283 dell optiplex i5 again with more ram?

Cheers,
John

[socratis]

The simple math that I would use:

• Host core CPUs: Total CPUs in concurrently running VMs + 1 (for the host itself).
• Host RAM: Total RAM allocated in concurrently running VMs + HostOS + ~1GB free (you never know).
• Host HD: That will depend on your setup. Don't know what you have in mind.

And also note that I have highlighted the cores in the system. Don't look at the hyper-threaded ones. They don't count.

BTW, I found server #1, I was not able to find server #2.

[Meatbeast]

ok, so that sounds like the older multi cpu server, 4 cpu's 8 cores is a better choice than the modern i5...

i cant post urls yet but if you search,

Dell Optiplex 3010 i5 3470 (4x 3.2 - 3.6GHz) 4GB, 500GB,Windows 10

in ebay there should only be one hit.

many thanks

[scottgus1]

4 cpu's 8 cores

It's important that the 4x8 or 6x12 concept not bite you.
There's cores in the chip and there's hyperthreads in each core. Thus an I7 might be 4 cores 8 threads, due to hyperthreading. For Virtualbox, only the physical cores count. So the I7 can only give 4 cores for host & guests, just like a non-hyper-threaded I5. Don't count hyperthreads or the AMD equivalent, only count physical cores.

The safest CPU usage, as Socratis pointed out, is make sure the count from all guests is one less than the total cores in the host (one less so the host has something to run on). And you might find that your guest may run better with one cpu instead of multiple. There's overhead to schedule instructions in a multi-processor environment, so a multi-processor guest is actually slower than a single-processor guest in pure number-crunching time, although the multi-processor guest may remain more responsive to user input when a running program is churning up a processor.

However, if the guests aren't going to be running full-blast number crunching all the time, and have good amounts of low processor usage, one may run more guests than one has processors for on the host. No guest should use all the processors in the host - if the host CPU is 4 cores, all guests should be 3 cores or less, etc. But I have run two 2-processor guests and a 1-processor guest simultaneously on a 4-core host with no trouble. (That's 5 guest cores and one for the host = 6, on a 4-core CPU.) None of the guests maxed out the cores for any heavy length of time, so there was always room for the other guests to run. Your guest usage, if not heavy, may allow more guests than the host would seem to be able to run by the safe-usage formula. If they all suddenly decide to hit the trench full-throttle to keep the fighters off their tails, then you'll have problems.

Disk bandwidth may be a problem if you have multiple guests running off one disk. My experience tells me to expect sluggish disk activity if you run more than two modern OS's on one platter drive. SSDs do make disk activity almost a moot point, if you can afford bigger disks.

Memory can't be cheated, it's simple math: Host OS needs + guests' needs < Host RAM. Couple of gigs for a host OS that's just running guests, more for the host if you run fancy programs on it while running guests. (If it's a Windows host, use Sysinternals' Process Explorer, Physical Memory graph, to see how much the host uses under normal and/or heavy usage.) The rest of the ram can be used for guests. Throw as much memory as you can afford at the host. (For Windows hosts, at least, keep in mind that the hibernation file on the host C drive will be the size of the host's RAM, so allow disk space for it when choosing the drive size.)