Posts Tagged ‘macintosh’

20th June

Using a virtual machine — perhaps VMware Fusion or Parallels Desktop — can result in way-too-large backups. Here’s one way to make those backups more manageable.

written by Mark Wheadon

If you’re using a product such as VMware Fusion or Parallels Desktop to run another operating system on your Mac (perhaps Windows or Linux), then you may have noticed that your backups are now taking a long time. I documented one approach to solving this problem in an earlier article. Now here’s a different approach, originally suggested by Chris Ryder (thanks Chris).

First, here’s a recap of the problem. It’s written in terms of VMware Fusion but should be equally valid for other VM engines such as Parallels Desktop. If you’ve already read the previous article then you might want to skip to the meat of this article.

Large backups

When you’ve been using Fusion’s virtual machine (in my case, to run Windows), you will find that Time Machine’s backup takes longer than expected — sometimes much longer.

This is because Fusion stores its virtual machines’ disks as a bunch of large files. When you run your virtual machine using Fusion (or Parallels Desktop), the contents of the VM’s virtual disk changes, and even if you haven’t made many explicit changes to files, all sorts of small changes happen to the virtual disk’s contents.

Incremental can still be too much

Time Machine performs incremental backups. That is, it copies only files that have changed since the last backup. Unfortunately those large files that Fusion uses to store the virtual disk’s contents? They’ve probably all changed, at least a little.

backupSo, instead of your incremental being a few megabytes and taking a few tens of seconds, it’s ten gigabytes, takes ages, and rapidly fills your backup disk. (Which causes its own problems: described here.)

One solution: back up the VM in another way

One solution is to keep all your precious files in the Mac file-store, tell Time Machine to avoid backing up your virtual machine(s), and then back them up some other way. This results in the smallest backups and is useful if you don’t need sophisticated incremental backups of your virtual machines.

If this sounds like you, then I’ve shown how this can be achieved in an earlier article.

An alternative solution: use a sparse bundle

If you need proper incremental backups of your VMs, then one approach is to use a sparse bundle. This is a disk image which is stored  as a collection of small files (typically 8MB), so when Time Machine backs up the disk image, it only needs to copy the files that have changed.

This approach still isn’t perfect — when (for example) Windows does anything, it tends to scatter its writes over the disk, so incremental backups are still large, but they’re not as large as when Time Machine backs up the VM directly. Typically, your incrementals may be a few hundred megabytes with no VMs, a few gigabytes with a VM stored on a sparse bundle (for Windows. Linux may be better behaved), and a few tens of gigabytes with the same VM stored in the standard way.

Here’s how

First lets create a new disk image based on a sparse bundle and move our VM onto it. We’ll need to know how large to make the VM, so go to Documents and look in Virtual Machines. In there is one folder per virtual machine and you can find the VM’s size by clicking on the corresponding folder and hitting cmd+I:

VM size

Create the disk image

Now create the sparse bundle. The point-and-click way of doing this is to use Disk Utility, so start that up (I use spotlight to do so):


and click on New Image:

Picture disk utility

Then fill in the details. I made my sparse bundle file-system for the Windows XP VM twice as large as the space it currently occupies, to allow for future expansion — so 50GB in my case (don’t worry: it only uses as much real disk as is needed to store the actual content). Here’s all the fields you need to change:

Bundle settings

  • The Save As is the filename for the sparse bundle whereas the Volume Name is the name the disk will have when mounted — I made them the same;
  • I saved my sparse bundle in Documents->Virtual Machines;
  • Image Format needs to be sparse bundle disk image, as that’s the whole point of the exercise.

Now click on Create, and

Creating image

a few seconds later you have a sparse bundle file-system image.

Mounted bundleNow double-click that file (mine’s called VM disk.sparsebundle).

Mac OS will mount it…

and the new file system will appear on the desktop.

Move the VM into the new disk image

Next, drag the folder(s) corresponding to the VM(s) you’d like backed up by Time Machine onto the new disk. Hold down cmd as you drag and drop, so that you move the folders (rather than copying them):

Move onto diskEnsure the new disk image is mounted at login

The .sparsebundle file needs to be mounted every time you log in, so that the file-store is available. To do that, go into System Preferences->Accounts, click on your username and then on Login items. Now drag your sparsebundle file into the list of login items:

Mount at loginand that’s it.

Using your newly-homed VM(s)

To use your new VM(s), just double-click on the corresponding folder — perhaps put an alias to it on your desktop or in the dock. When you next use it you’ll get a message:

I moved it

Just click on I moved it and you’re sorted.


As with any method of backup which relies on backing up the virtual machine’s disk image using the host operating system, your backup may not be of any use if it’s made whilst the VM is running, so I suggest you make sure that Fusion/Parallels is not running when Time Machine is backing up your data. If you don’t always manage to do so then some of your backups may not be valid.


Because if you backup the files that Fusion (or Parallels) is using for a disk image, then you’re backing up what’s on disk, but not what’s in memory, in disk buffers, etc. So when you come to restore from backup, you may find that the disk image is corrupted. In the worst case scenario you won’t be able to start up the VM’s operating system successfully at all, or restore any files contained within the VM’s file-store.

By backing up when the VM isn’t running, you ensure that all data is on disk in a safe, consistent state.

1st March

How do you dump the screen in Mac OS X when you can’t reach for a hot-key-chord? The answer is grab.

written by Mark Wheadon

Mac OS X Leopard has a tool to dump all or part of the screen built into the desktop, with handy (if difficult to remember) hot key-chords:

  • cmd+shift+3 to dump the whole screen
  • cmd+shift+4 to select an area of the screen (then press space for a whole window).

However, there are times when the above won’t do. Typically, it’s when you’re already pressing keys to get the image you need — the key chord cmd+shift+4 isn’t going to work if you’re already holding down alt for example.

That’s where grab comes in — it’s what Mac users used before cmd+shift+3/4 came along, it’s still there, and it can dump the screen after a ten second delay.

So, start up grab. I use Spotlight to do that, so I type cmd+space grab:

spotlight grab

Then, to do the delayed screen dump, select Timed Screen from grab‘s Capture menu:

grab timed screen dump

You then have ten seconds to set up the screen as needed, and grab does the rest.

Then select File->Save As… to save the resulting tiff file, and you’re done.

22nd February

Always open a file with a particular application in Mac OS X — the easy way.

written by Mark Wheadon

press alt

First, the hard way

When you wish to open a file using a particular application, it’s simple. Just right-click on the file (ctrl+click) and select Open With.

open-withHowever, if you’d like that file to always open with the selected application then things are less elegant: right click, Open With, Other…, select the application and tick Always Open With. Fiddly.

The easy way

Fortunately there is an easier way.

Right click on the file as before, but this time depress the alt key. Hey-presto, the Open With option changes into Always Open With.

always-open-withHow’s that for handy?

Changing the default application for all files of a kind

The above method sets the default application for this file only. If you’d like to change the default application for all files of a type (a kind in Mac OS speak) then here’s how to do it.