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I would like to buy a dedicated server and virtualize it. Details:

Host OS Ubuntu 12.04 server OS Setting up 3 VMs. 2 serving web applicaitons with php/Mysql + nginx and 1 running bugzilla.

With that said how much RAM memory should I allocate for the host OS. The host OS will not be used for anything other than managing the VMs. Please let me know if I need to supply more info. I am planning to use KVM for virtualization.

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marked as duplicate by Bryan, Mark Henderson Jun 24 '13 at 12:13

This question was marked as an exact duplicate of an existing question.

Ubuntu 12.04 Desktop or Ubumtu 12.04 Server OS? – tombull89 Jun 24 '13 at 10:30
@tombull89 Ubuntu 12.04 Server OS – sunlover Jun 24 '13 at 10:33
How many concurrent users have you estimated? have you considered to provision nginx in a different VLAN (and a different VM) that MySQL? – dawud Jun 24 '13 at 11:11
@dawud - nginx/php-fpm/mysql would reside in a guest VM. They will not live in the Host OS – sunlover Jun 24 '13 at 11:56
Note that unused RAM on a VM host is not necessarily a waste. As a Host OS, Linux will use any unused RAM for disk cache, so what the VM think is disk access may in fact be served by a much faster RAM access on the host. – Lie Ryan Apr 21 at 17:56

You would need enough RAM for 3 VMs and some more for the host.

For the host

2GB of RAM plus additional RAM for guests.

For the guests

This depends on your needs. Most entry level VMs have around 1GB of RAM nowadays so that should server as a good starting point if you're not sure.

If you wanted to keep things lean (and your server won't have a lot of visitors/users) you may get away with less (you could try for 512MB RAM). Keep in mind the moment you start installing software, and getting visitors/users you'll need to cater for more RAM.

Until you do your own tests you won't really have a real indication of how much RAM each machine will need, and of course this will change as your server usage changes.

Here are some good questions to consider:

  • How many visitors will the server need to handle?
  • What sort of scripts will the server be running (custom scripts or add-ons may increase the amount of grunt required).
  • Will you have big databases or datasets?
  • Will you need to do things like AntiVirus Scanning, Backups or Maintenance tasks (these will consume RAM)
  • Will you take advantage of software like Varnish (this may help reduce the amount of work PHP has to do, thus reduce your need for RAM on that box)
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I am trying to find out the RAM neccessity about the Host Os and not the guest OS. – sunlover Jun 24 '13 at 11:57
I have explained the requirements for the host. – Drew Khoury Jun 25 '13 at 1:16

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