Time Machine vs. CrashPlan for Backups

Trouble in Time Machine Land

In my recent article, A Simple and Effective Backup Strategy for Mac OS X, where I recommended a three part backup system: 1) a full disk clone, 2) local incremental backups with Apple’s Time Machine, and 3) networked incremental backups with CrashPlan. I found Time Machine problematic for my own setup, for reasons I explain below, so I now use CrashPlan for both local and networked backups.

For most people with configurations that are not highly customized or complicated, Time Machine is a great “set and forget backup” solution. The primary interface is a single on or off toggle switch. Its ease of use can make the difference between having backups and not having backups for many. At the same time, Time Machine has some notable quirks and limitations that can make it far less desirable in some circumstances. In these cases CrashPlan provides a solid alternative for local backups in addition to network backups. CrashPlan also has the advantage that it works equally well on Windows and Linux.

Clones are Key to Fast Recovery Time

Let me emphasize that maintaining a recent clone is the key for you to rapidly recover your data in the case of a disk failure or theft. Most incremental backup solutions, including Time Machine and CrashPlan, do not backup your entire computer including all the system files and boot records. This means that you must first reinstall your operating system and then restore your files from the incremental backup on to the newly installed operating system.

The process of recovering from a disk failure with a clone is much faster and more efficient since you can connect your cloned disk and boot from it. You computer will be in the same state as it was when you made the clone. You will only have to restore files that have changed since you last made the clone. No other recovery process is nearly as quick recent clone and an incremental backup. The difference is substantial.

Advantages of Time Machine

  • It’s free, supported by Apple and ships with every copy of Mac OS X
  • The setup is impressively simple and it generally just works after that
  • The overall user experience for backup and recovery is substantially better than most alternatives
  • You can manually mount a Time Machine disk on any computer and copy files from it

Disadvantages of Time Machine

  • When you restore from a Time Machine disk, the backup is invalidated and you must start your backups anew
  • Time Machine only backs up changes to your files once an hour, so there is always a potential lag in your backups
  • If you use FileVault, Time Machine will only backup your home directory when you log out
  • If you use FileVault, you can only restore your entire home directory (missing out on the great restore interface) unless your home directory is on Mac OS X Server
  • Time Machine can get confused if you plug more than one Time Machine backup disk into the computer
  • Moving a backup to a new computer is a complicated process and typically requires editing system files

Personal Observations About Time Machine

  • The combination of FileVault and Time Machine makes logging out very slow
  • I found the Time Machine volume occasionally got corrupted and I would have start over
  • Time Machine would sometimes cause large amounts of disk IO with high memory usage that substantially slow my machine down. This would typically happen after longer periods of not backing up due to travel etc.

Advantages of CrashPlan

  • Backups are continuous and files are backed up as soon as they change (note while CrashPlan can be used in local mode for free, continuous backups require a subscription to CrashPlan Central)
  • All backups are encrypted by default
  • Straightforward to configure multiple local and networked backup destinations

Disadvantages of CrashPlan

  • You must use the CrashPlan software to restore a backup, it needs to be installed first for recovery
  • Higher memory usage with 64-bit Java on Snow Leopard (see note below)
  • User interface is functional but, not nearly as nice as Time Machine, it’s also a bit slow to start up
  • If you use FileVault, you must be logged as the FileVault user for backups to happen

Personal Observations About CrashPlan

  • Simple fix improves memory usage
  • Appears to have much smaller impact on my system resources once memory is reduced
  • FileVault complicates install process

Notes on Reducing CrashPlan Memory Usage

I found that CrashPlan could use up significant amounts of memory with the 64-bit Java on Snow Leopard. The most recent version of CrashPlan places a 512 MB memory limit on the process, but that is still quite large. I limit my to CrashPlan process to 150 MB and it has not caused any problems, although this is lower than you will generally see recommended and you will want to carefully monitor your logs to look for memory errors if you set it this low. This post CrashPlan using too much memory on Mac OS X from offTheHill explains how to reduce the memory footprint of CrashPlan.

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