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How Time Capsule and Time Machine Work And What Should Be Excluded From Backups

written by: Nicholas•edited by: Michael Dougherty•updated: 12/8/2009

Apple's Time Capsule is an obvious choice for backups on a Mac computer. It works seamlessly with Time Machine, and is a near plug and play solution for wireless backups. However, some applications such as VMware Fusion and Parallels do not cooperate very well with Time Machine backups.

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    How Time Capsule and Time Machine Work


    The first time you use Time Capsule (or any other external hard drive for backup), Time Capsule copies the entire contents of your Mac's hard drive, to its built-in hard drive. This process can take several hours the first time, depending on how much info you have on your hard drive. From then on, any new backups that Time Machine makes will only copy new information that has been added to your Mac's hard drive since the last backup. For example, if you add a 2.75MB MP3 file to your Mac, the next time that Time Machine backs up your info, it will only need to backup 2.75MBs worth of information, which should only take a couple of seconds. Time Capsule and Time Machine work by detecting changes among files on your Mac and backing up those changes every time Time Machine is running.

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    Problems With Time Capsule 

    The problem with this method of backup is that some applications do not work properly with the "schematics" that Time Capsule uses.Two well known apps that can mess up Time Machine backups are VMware Fusion and Parallels. When you create a virtual machine via VMware Fusion or Parallels, you are adding quite a bit of information to your Mac. And, every time you add new apps or files to the virtual machine, you are adding even more info.

    This creates a problem with Time Machine. As stated above, Time Machine backs up any files that have been changed or modified after its last backup. When any file or slight modification is made in a virtual machine (in Parallels or Fusion), Time Machine recognizes this modification as a change to the entire virtual operating system. Thus, Time Machine backs up the entire virtual machine.

    This causes Time Capsule to fill up extremely fast. If you had a virtual machine that was 100GB in size, Time Capsule would backup the 100GB plus any modifications, every time Time Machine runs, which by default is every hour. At this rate, your entire Time Capsule would fill up in a matter of days.

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    More Info

    The best way to stop this problem with Time Machine and Time Capsule is to exclude your virtual machines from backup. Be sure to read part 2 that details the steps in excluding items from Time Machine backups and also provides further advice.

Time Capsule / Time Machine Application Backup Fixes

Time Machine and Time Capsule are two great Apple products that work very well at backing up a Mac computer. However, there have been some bugs and discrepancies with Time Machine working with certain applications. This article explains how to exclude items from backup and suggests files to exclude.
  1. How Time Capsule and Time Machine Work And What Should Be Excluded From Backups
  2. How To Exclude Items and Applications From Time Machine Backups