Some people will be able to set up and turn on Time Machine with a single click. But you may need to do some manual configuration to get it to work the way you want. You should also be aware of some quirks in Time Machine’s operation, particularly when restoring data.
Get set up right
When you first plug in a hard drive that’s suitably partitioned and formatted, Time Machine displays an alert asking if you want to use that disk for backups (see “One-Click Backup”). Click on Use As Backup Disk—that’s the one-click setup—to turn on Time Machine and set it to use that hard drive as its destination.
If no alert appears, or if you want to choose a network volume as your destination, open the Time Machine preference pane and click on the Choose Backup Disk button (which switches to Change Disk after your initial selection). Select the volume you want to use and click on Use For Backup. Follow the same procedure if you want to use more than one backup disk and switch between them; after connecting the new drive, select it in the Change Disk dialog box.
If your backup disk is too small to hold all the files on your startup disk, you can tell Time Machine not to back up some of them. To do this, click on the Options button in the Time Machine preference pane. Then either drag the items you want to exclude into the Do Not Back Up list from the Finder, or click on the plus-sign (+) button, navigate to a file or folder, and click on Exclude.
Here are some suggestions:
System Files The files that make up OS X itself—including programs such as Safari, Preview, and iCal—take up nearly 10GB. To exclude all of them, add your System folder to the Do Not Back Up list. Click on Exclude All System Files when prompted. Note that excluding these files means Time Machine will be unable to restore your entire disk—but if you maintain a separate bootable duplicate, that shouldn’t be a problem.
Large Media Files Video files and, to a lesser extent, audio files can take up an enormous amount of space. Consider excluding folders containing such media files if you can recover them in some other way.
Virtual Machine Disk Images If you use the $80 Parallels Desktop 3 ( ) or the $80 VMware Fusion 1 ( ) to run Windows on your Mac, you may have one or more large disk-image files that contain an entire Windows installation. These files change every time you do anything in Windows, so you should back them up separately. You can find Parallels disk images in your user folder/Documents/ Parallels/virtual machine name (look for files with the extension .hdd). For Fusion, look in your user folder/Documents/ Virtual Machines (Fusion disk images use the extension .vmwarevm).
Installers Downloaded software, typically distributed in disk-image files, can chew up disk space quickly. Exclude your Downloads folder to give Time Machine more breathing room.
Aperture Files At press time, Apple reported conflicts between its photo-management program and Time Machine. The company recommends excluding your Aperture library.
Control ons and offs
Time Machine ordinarily runs in the background, updating your backup disk once an hour. If you want to disable automatic operation temporarily (for example, to reduce disk noise or improve the performance of other disk-intensive tasks), click on the on/off slider in the Time Machine preference pane. Whether that slider is in the on or off position, you can force Time Machine to do an immediate backup by right-clicking (or control-clicking) on the Time Machine icon in the Dock and choosing Back Up Now from the contextual menu.
Note that you do not need to turn off Time Machine before disconnecting or unmounting its destination disk.
Fix unrecognized disks
If you attach an external USB or FireWire drive and its volumes do not show up in Time Machine, or backups proceed partway and then fail, one likely reason is that the drive was originally configured for Windows and, for one reason or another, Time Machine can’t reformat the drive automatically. Ordinarily, Windows-formatted drives work fine in OS X, but Time Machine is pickier—it requires that destination volumes be formatted as Mac OS Extended (Journaled) (see “Volume Format”). In addition, the partition map scheme must support the format and size you want to use for your backup volumes.
The partition map scheme describes how the drive stores its volumes. Drives originally set up for use on Windows usually use the Master Boot Record (MBR) scheme, as opposed to the Apple Partition Map (APM) scheme, the default for PowerPC-based Macs, or the GUID Partition Table (GPT) scheme, the default for Intel Macs. Although OS X supports MBR, there’s a catch: Mac OS Extended volumes can be no larger than 512GB on a drive partitioned with the MBR scheme. So if you have, say, a 750GB or 1TB drive, you must repartition it to use the GPT or APM scheme before it can work with Time Machine.
Disk Utility can identify your drive’s partition map scheme and format and change them if they’re incorrect. Open Disk Utility and select your external drive in the list on the left. In the lower right corner of the window, you should see the words Partition Map Scheme (see “The Right Partition Scheme”). If it says Master Boot Record and you have a backup volume larger than 512GB, you must repartition the drive. To check on the format of any volume on the drive, select that volume in the list on the left. At the bottom of the window, next to Format, you should see Mac OS Extended (Journaled) or Mac OS Extended (Case-Sensitive, Journaled). If you see anything else, you must reformat that volume.
First, a warning: repartitioning erases all the data on your drive; reformatting erases all the data on the volumes you’re changing. To repartition your drive, select its icon in the list and click on the Partition tab. Then choose the number of partitions you want (even if that number is one) from the Volume Scheme pop-up menu. Select each partition you just created, type a name, and make sure the Format pop-up menu says Mac OS Extended (Journaled). Then click on Options. In the dialog box that appears, select GUID Partition Table if you’ll be using the drive only with Intel Macs; choose Apple Partition Map if you’ll be using it only with PowerPC Macs or with both processor types. Click on OK. Finally, click on Apply. In the confirmation dialog box that appears, click on Partition.
If your drive’s partition is correct but the format of one or more of the volumes is not, select the volume you want to reformat in the list. Then, in the Erase tab, choose Mac OS Extended (Journaled) from the Volume Format pop-up menu and click on Erase. To confirm your choice, click on Erase in the dialog box that appears.