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I have an OS X / Windows 7 RC dual boot setup. On the same hard drive those OS's are installed on, I have a FAT32 partition. I have an Ubuntu Server 64 virtual machine that I created in VirtualBox in OS X and I located the VDI on the FAT32 partition. I followed some instructions to setup the same virtual machine in VBox in Windows 7 and pointed it to the same VDI.

Is it possible for me to use the same settings file for both hosts (OS X and Windows 7)? Since I'll always need the settings for both hosts to be the same, it would be great if I could just put a settings file on the FAT32 partition and point VBox on both hosts to it.

Look in the Manual, there is an environment variable you can use for this, or just edit the xml files so they point at the same location.

The use of the same settings file will not work because of the differences between Windows and Mac. Windows has other paths, sound system and NIC names. What you need, is separate settings file for the VM with the same structural settings (MAC address etc.), but a generic location for both systems. Now for that location, you will hit a very big issue quite early on. Your VM will surely grow beyond 4 GB and that is something it can't do because it's on FAT32. Mac OS can access NTFS drives just fine if you install NTFS-3g. It's stable enough now and installed by default on Linux. The only thing you must NOT do with that shared drive is defragment it. The disk check it triggers can cause data loss. I've lost my VDI files a few times because of that.

Sasquatch wrote:Your VM will surely grow beyond 4 GB and that is something it can't do because it's on FAT32.

Thanks very much for pointing that out to me, I was oblivious to that. I took a look into NTFS-3G, and judging by the comments on the blog and forum, people seem to have a fair amount of issues with it, at least on Snow Leopard, which is what I'm running. I will have to solve that problem at some point, but I'm a bit leery of NTFS-3G based on what I've read so far.

Sasquatch wrote:What you need, is separate settings file for the VM with the same structural settings (MAC address etc.), but a generic location for both systems.

You mean a separate settings file -- with duplicated settings -- for each host, and a common VDI file, right? That's the setup I have right now. By "generic location" you mean a shared VDI file, right? Or are you saying there is some way to have a common settings file for both hosts?

I currently have a separate settings file for each host, both configured with the same settings. It's just unfortunate that if I have to change any setting I'll have to boot into each host OS and change the setting twice.

Sasquatch wrote:The only thing you must NOT do with that shared drive is defragment it.

So it would be wise to put it on a separate NTFS partition from my Windows installation?


Thanks Sasquatch!

Badger wrote:

Sasquatch wrote:Your VM will surely grow beyond 4 GB and that is something it can't do because it's on FAT32.

Thanks very much for pointing that out to me, I was oblivious to that. I took a look into NTFS-3G, and judging by the comments on the blog and forum, people seem to have a fair amount of issues with it, at least on Snow Leopard, which is what I'm running. I will have to solve that problem at some point, but I'm a bit leery of NTFS-3G based on what I've read so far.

I think they used it to mount their system drive and they did a few things that aren't advised to do. Like I said, a defrag can cause a check disk which could result to data loss. Windows defrags when the system is idle in the background. Can be disabled though.

Sasquatch wrote:What you need, is separate settings file for the VM with the same structural settings (MAC address etc.), but a generic location for both systems.

You mean a separate settings file -- with duplicated settings -- for each host, and a common VDI file, right? That's the setup I have right now. By "generic location" you mean a shared VDI file, right? Or are you saying there is some way to have a common settings file for both hosts?

I currently have a separate settings file for each host, both configured with the same settings. It's just unfortunate that if I have to change any setting I'll have to boot into each host OS and change the setting twice.

Yes, one settings file for each OS, as you have now.

Sasquatch wrote:The only thing you must NOT do with that shared drive is defragment it.

So it would be wise to put it on a separate NTFS partition from my Windows installation?


Thanks Sasquatch!

Yes, it's best to have a separate partition for shared data. Not only will that keep your data when you need to reinstall Windows, it will also keep your OS fast(er) because non-OS data will not clutter the partition which will only increase the search time.

Badger wrote:I will have to solve that problem at some point, but I'm a bit leery of NTFS-3G based on what I've read so far.

If you are uncomfortable using an NTFS partition then a possible alternative is to use "VBoxManage clonehd" to convert the VDI into a VMDK, making sure to use the "--variant Split2G" option, causing the VMDK to be split into 2GB chunks - meaning you can keep the VMDK on a FAT32 partition. I should warn you that I've never tried that particular variant of the clonehd command, but it should work.

Obviously if it does work then you'll need to register the new VMDK and mount it in your VM instead of the existing VDI.

You can also create multiple VDI files of 3,5 GB each and mount them in the Guest OS on locations. E.g. one VDI for /usr, one for /home, one for the rest. Maybe /usr in itself will become too big and needs to be split, but that's not a big issue.

But, if possible, use NTFS. If you're unsure, make a test VM that can break and make heavy use of the NTFS partition. When there is no problem, you can then make your final VM on it.

Thanks for the additional suggestions mpack and Sasquatch.

I think I'll give NTFS-3G (or something similar) a shot. I guess that seems like the most straighforward solution. I should probably do something soon, because my VDI is already over 3GB. Thanks again for warning me about that, Sasquatch.

I wasn't going to ask, but I can't help it, I'm too curious: why can't you defragment the shared NTFS partition? Is the problem specific to the VDI files, or it's more general than that?

Sasquatch wrote:If you're unsure, make a test VM that can break and make heavy use of the NTFS partition. When there is no problem, you can then make your final VM on it.

I don't think I'd have the patience for that, and it wouldn't be reliable. I think I'll just have to backup my VDI periodically in case of trouble.

Badger wrote:I wasn't going to ask, but I can't help it, I'm too curious: why can't you defragment the shared NTFS partition? Is the problem specific to the VDI files, or it's more general than that?

I think it's more of a general thing, because I had it on drives that didn't have a VDI on it, or I didn't run a VM in a long time.

Ok, well thanks for your help.