How much RAM is recommended to be assigned to a virtual machine in VirtualBox?

[tim12]

I have installed Ubuntu in VirtualBox under OS X on a MacBook Pro.

The laptop has 16 GB RAM, and I assigned about 11 GB to Ubuntu, because I thought that most work would be done in Ubuntu anyway.

But some said that I have to give OS X sufficient RAM, to maintain Host regular operations.

Is 5 GB too little for OS X?

I noticed that when the guest Ubuntu is running, waking up of OS X from sleep can take 30 secs or so. If OS X can have more RAM, will it wake up sooner?

Thanks.

[michaln]

This is not a question that can be answered in a generic way. On 16 GB host, giving the VM more than 8 GB is probably not a good idea. Probably. It all depends on what you need to do on the host and what you need to do in the guest. And obviously it also depends on how many VMs you'll be running at the same time.

You won't get any specific recommendation beyond "try various settings and see what works best for you".

[scottgus1]

Giving the supermajority of host ram to a guest (or guests) is not necessarily a problem. I have run guests taking 28GB ram from my 32GB host with no problems. The "use only half" idea is probably to help newer users to not get into trouble quickly.

If your host is only going to be hosting guests and not doing much itself, you can probably use a memory tool to see how much memory the host takes just sitting there after bootup. Add a GB or two for a comfortable margin, and use the rest for guests, or one really big guest. If your host is going to do a lot, then load it up before starting a guest and see what it takes out of ram, then add the margin and use the rest for the guests. (Of course, a guest that doesn't do much isn't going to need tons of ram. XP can easily get by with a half-GB when just used for browsing and email, whereas a domain controller Server & Exchange email server guest may need a dozen GB or more.)

to quote MichalN:

It all depends on what you need to do on the host and what you need to do in the guest.

And fortunately it takes just tweaking the memory if you find that something gets sluggish.

[socratis]

+1

The "use half of your (available) RAM" I believe is an anachronistic term from the times that 2GB was the norm for the host. Yes, it could make sense at some point in time. Your thought on not putting the host on stress is the rule that I follow as well. Whatever that means depending on the occasion.

[scottgus1]

I noticed that when the guest Ubuntu is running, waking up of OS X from sleep can take 30 secs or so.

This is because there's an 11GB guest running and all that active memory must be stored to or pulled from disk to preserve the guest through the host sleep.

[Smackey's dad]

This is a fairly easy question. Allocate as much memory required by the Guest Operating System. I have multiple Ubuntu OS running under 512 MB of RAM for over a year. Ubuntu requires a minimum of 512 MB, but I run under that requirement and sometimes as low as 128 MB because it works. I had to disable automatic apt-updates (http://tech.snathan.org/tech/linux/apt_ ... e_overload) as they were a memory hog when those cron jobs ran. This question has nothing to do with Host/Guest/VirtualBox and everything to do with the Guest memory requirements without regard to the fact this is a VM.

[scottgus1]

Allocate as much memory required by the Guest Operating System

Squeeze the host too much and it will have to start thrashing to the hard drive's page file, slowing host processes. At least the throughput of the hard drive will suffer, which may impede the guest if its virtual drive is on the same physical drive as the host OS.

It's all a balance, and involves testing, especially for production hosts.