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

Question

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?

To start an answer, it would be helpful to know two things. 1. What is your level of comfort running VM_stat on Linux to check for virtual memory paging activity and swap file usage? 2. Are you using your phone to as a main desktop machine where it's fullscreen and lots of apps will be running. Or are you going to have multiple guest operating systems running in the background and doing most of the work on the Mac? — bmike, Jun 12 '16 at 15:06
Wonderful - this might be candidate for closing as too broad - let's try an answer and you can ping me in the [chat] or we can find some related questions to go over concepts for you. — bmike, Jun 12 '16 at 15:25

score 2 · Answer 1 · edited Apr 13 '17 at 12:45

My best practice is to think about how to get the best use of your RAM and not make configuration decisions that lock down memory and instead monitor for problems on each OS and then make small adjustments.

On the Mac - open Activity monitor and watch the memory pressure. I would try to keep things in Green. If you are in the orange, that's ok, but you might want to try changing the reservations (less RAM to ubuntu guest or quit apps on either OS that take most active memory). In the red, you will be swapping and slowing down the response times.

So - you have 16 GB of RAM and one OS X running the hardware with Ubuntu running in Virtual Box. Virtual box makes a file or files to act as the storage for Ubuntu but OS X is handling all the actual reads/writes.

Second - both Ubuntu and OS X use virtual memory so that you could allocate 1 GB of Ram to the guest OS and it will use a swap file to make more memory as needed.

To initially monitor things, I would open terminal on both the host and guest and run something like vm_stat 5 - pay attention initially to only two numbers - the free and the swap out. Also pay attention to the memory pressure on OS X.

Over time, you can shift to logging things more slowly with vm_stat 60 / vmstat 60 or even time stamp the usage.

Since free memory is a waste on both OS X and Ubuntu - you will want to allocate all the RAM to OS X so it can cache all the file input and output for both OS X and virtual box. Allocating too much memory on ubuntu will make the OS X starved for RAM to cache the guest OS. Add memory to the guest OS when the applications you run there start to swap out to disk.

Here are some links to get started on tuning and learning:

Thanks. Is the amount of memory that I specified when creating the virtual machine for the guest Ubuntu reserved for the guest Ubuntu, and not available for host OS X to use, even when most of it is not used by the guest Ubuntu yet? — Tim, Jun 12 '16 at 16:49
Is it correct that the RAM for a virtual machine adjustable? — Tim, Jun 12 '16 at 16:59
In Ubuntu, it is vmstat not vm_stat. I used free before. — Tim, Jun 12 '16 at 17:04
Yes - that's why I put "with vm_stat 60 / vmstat 60 " to show the differences. It's too broad to explain all of virtual memory here. Basically, when you configure the VM to get 11 GB you remove that completely from OS X side so make that smaller and only change it up when ubuntu is slow or has memory errors / swapping. — bmike, Jun 12 '16 at 17:06

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

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