How many Virtual Machines on 1 host

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tatbaird

142 posts

Master Geek

#90682 27-Sep-2011 20:05

Anyone with experience running multiple virtual machines on one host? Specifically VMware workstation running server 2008 under win7 64. Core i7 920 and 6 gig ram. You reckon I could squeeze five simultaneous VM's out of that? That'll be a server base, 2 full clones and two linked clones.

Cheers.

kyhwana2

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#526470 27-Sep-2011 20:56

5 VMs? All depends on what they do and how much RAM they need. You might be hitting IO limits if you're just running it off a single spinning drive.

tatbaird

142 posts

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#526525 27-Sep-2011 22:20

Mostly I'll just be working on various server concepts. I figure around a gig of ram per instance. There shouldn't be too much hard disk usage for anything. Anyway, I suppose it'll just be trial and error.

Zeon

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#526533 27-Sep-2011 22:32

6GB isn't too much but it may be OK if you give each VM 512MB or so. Put it this way we upgraded from 16GB to 48GB on one of our main hosts due to RAM limitations.

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networkn

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#526548 27-Sep-2011 23:13

If it's just for testing I would think 512 to 1024MB per server (Without additional things like exchange) and 256MB for every xp machine

gzt

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#526571 28-Sep-2011 01:58

I have done that sort of thing on lesser spec machines. Main thing is have your o/s on a different drive from the vm storage area. If there is not a lot of disk access going on you will be a-ok.

If you have more disks available to separate your non-linked vm's further, that's even better.

timmmay

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#526620 28-Sep-2011 09:21

It really depends what you're doing with the servers. Figure 515MB-1GB per VM for the OS, plus whatever software you're running. You might get away with it if the unused code is swapped to disk, it's hard to say.

I ran 3-5 VMs for development work once, it went a lot faster when I went from 8GB to 16GB RAM.

tonyhughes

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#526635 28-Sep-2011 10:00

Think about your bare minimum requirements for RAM, then double it. Agree with posts above re: spindles. Get the machines on different disks - certainly your production machine(s) anyway.

Re number of machines? Have gone crazy and run many VMs before, but my advice is to run ~5, depending on your hardware and software specs and requirements. If you just want a bunch of XP instances doing 5/8ths of not very much, by all means, stick 10 of 'em on there. If you are starting to do grunt work anywhere, think about RAM, disk access, LAN throughput, and CPU time required, and you may start revising the number of VMs down quite quickly.

Note: Just realised this is for VMWare workstation. I'd say max 5 in any case on the desktop, although I haven't virtualised anything for a couple years now.

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tatbaird

142 posts

Master Geek

#526801 28-Sep-2011 15:25

Ok, thanks a lot guys. Some valuable info here especially moving things around to separate drives. Hadn't considered that. I'll see how it goes with 6 GB ram and if things get sketchy I'll consider an upgrade. Bearing in mind also that this is just a test environment on my home PC. Not only that but I'll also want to be running some GNS3 routing simulation as well as a VM'd Apache server. On second thoughts I'll probably have to shell out for another cheap laptop or two to get thing running sweetly.

Cheers

tonyhughes

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#526803 28-Sep-2011 15:26

Any money spent on secondhand laptops is better spent on more RAM if your system can handle it.

timmmay

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#526804 28-Sep-2011 15:30

Laptops would be a pretty bad way to go I think. Slower processors, slower disks, and more expensive. A modern CPU with plenty of RAM and disks would be better.

Moving from one to two disks made a huge difference for our VMs. One disk per VM would be good, if it was loaded at all.

gzt

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#527850 30-Sep-2011 20:02

Forgot to mention - Tip: if/when you are installing o/s, set the memory very high, it completes in good time. After you have it installed and configured how you want then reduce the memory in traditional increments as low as you can get away with for the function of the server. You can nearly get away with murder. If something just needs to sit there and service domain logon requests and authenticate a few things you can get away with well below the minimum specified. Don't try this at work ; ).

tatbaird

142 posts

Master Geek

#527968 1-Oct-2011 10:52

"Forgot to mention - Tip: if/when you are installing o/s, set the memory very high, it completes in good time. After you have it installed and configured how you want then reduce the memory in traditional increments as low as you can get away with for the function of the server. You can nearly get away with murder. If something just needs to sit there and service domain logon requests and authenticate a few things you can get away with well below the minimum specified. Don't try this at work ; )."

Beautiful, thanks. I'm still waiting for my desktop to be shipped here from my previous location. Will be here next week. When I've got it I'll play around and post results and conclusions here for anybody's future reference. Cheers guys, there's a lot of good info here.

tatbaird

142 posts

Master Geek

#560017 20-Dec-2011 17:13

Well ok, for anyone interested and reading this. Cheers again for all the suggestions. As of right now I have 7 VMWare virtual machines running simultaneously, all on the same drive, using around 7GB ram. That's 2 DC's and one file server (server2008) 3 clients (2 XP and one slackware) and one Apache server (red hat). I'm finding the use of only one spinning drive not really a problem as there really isn't a lot of I/O going on at the same time from all machines. Additionally I've got all VM's clouded in to GNS3 with routing set up, as the only painless way to integrate this with GNS3 is to have all machines on different host only VMnets. I tried for two days to get Virtualbox running as sweetly, but I found networking in Vbox problematic.
This kind of setup is pretty cool for anyone chasing certs or just looking to practice or test out networks before deployment. You can play around with different scenarios, topologies and configurations on multiple OS platforms, AD, Exchange, Routing, Web serving, whatever.