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Using Apple's Target Disk Mode with FireWire (IEEE1394)
By Brian Karr
ABSTRACT: Apple has provided a useful feature on their FireWire equipped computers, since May of 1999 with OS 8.6, called Target Disk Mode (TDM). This allows users to make their Macintosh internal hard drive appear as an external FireWire hard drive to another FireWire-enabled Mac. There are many uses for this beyond copying files between machines. This article outlines this and a number of other uses of TDM. In particular, system backup and restore, disk troubleshooting and repair are explained. Additionally, TDM will present any optical drives, to another Macintosh, which can be useful for MacBook Air owners or for Mac's that have older optical drives that, for example, do not support dual-layer DVD's. It's also a time-saving feature for those who want to upgrade to a larger hard drive, or to migrate files and settings to a new Mac. Most, if not all, of the tools you will need for all of this are included in OS X.
Target Disk Mode. Apple has provided a useful feature on their (IEEE1394) FireWire equipped computers, since May of 1999 with OS 8.6, which is called Target Disk Mode (TDM). This allows users to make their Macintosh internal hard drive appear as an external FireWire hard drive to another FireWire-enabled Mac.
Note that this should not be confused with “Target Display Mode” which allows you to use another Mac as an additional external Display (see the Links section below for more information).
Benefits. Target Disk Mode is more useful than other connection methods, such as Ethernet, because support for this is built into the Mac Firmware and therefore does not require a working operating system on the target computer. This lets you also troubleshoot a faulty system installation, perform a new install, run disk repair tools, backup and restore files or entire partitions, or access optical drives on the target Mac.
Being FireWire, this is also a very fast interconnect with most Mac’s in use today supporting the “1394b” 800Mbps FireWire signaling rate.
The target Mac. Enabling TDM on a Mac makes it the ‘target.’ To enable TDM on your target Mac, open System Preferences, click on the Startup Disk preference pane, and click the Target Disk Mode button. OS X will then prompt you to allow it to restart the computer. When it restarts and displays the FireWire logo, it is now a target Mac, and you’re ready to connect it to the Host Mac. Alternatively, you can hold the ‘T’ key on the Mac after the chime when you restart the machine.
To exit TDM on the target Mac, press the power button on the target Mac to shut down. Make sure to eject or safely remove any writeable volumes on the host computer first, see below.
Access CD/DVD drives and other volumes on another Mac
Accessing files. Mac’s which connect to another Mac in TDM mode will be able to see the optical drive of the target Mac when there is a disc in the drive. If you are using a Macintosh such as a MacBook Air which lacks an optical drive, or if you have an older Mac that doesn’t support dual layer DVD’s, then you can use this method to access the drive as you would an internal optical drive.
Booting from target volumes. Note that you can restart the Host Mac and hold the Option key after the chime, and you will be able to boot from the DVD in the target Mac. Similarly you can boot from the hard drive of the target Mac as well, but this is not always useful unless both machines have similar hardware configurations.
OS X Host. When you connect the target Mac to a host Mac, any hard drive volumes will appear on the Desktop and in the Finder as separate volumes. If you had a disk in the optical drive, it will also appear as a volume. If you “Eject” the Desktop volume that represents the optical drive, it will physically eject the disc from the optical drive on the target computer and you can insert another disc and read it if you like. Make sure to “Eject” any TDM hard disk volumes before disconnecting or powering off the Target Macintosh.
Windows Host. FireWire-capable Windows computers will see the target Mac as an “SBP-2 compliant device,” i.e. an external FireWire hard drive, and will prompt you for what to do with the volumes Mac. If there are multiple partitions on the hard drive you will see them as separate volumes. You can see them in the “Computer” view in Windows Explorer. While Windows 7 can read Apple native “HFS” formatted disk partitions, earlier versions of Windows may need a third party utility, such as Mac Drive to read HFS drives. Make sure to “Safely Remove” any TDM hard disk volumes before disconnecting or powering off the Target Macintosh.
Apple provides a lot of support articles for TDM on their support website , such as “How to use and troubleshoot FireWire target disk mode” http://support.apple.com/kb/HT1661
Linux Host. Linux distributions based on kernel versions 2.4 and later can read Apple native HFS partitions. Many modern desktop Linux distributions will mount the volumes found on the target and allow drag-and-drop of files seamlessly. Make sure to sync and unmount any TDM hard disk volumes before disconnecting or powering off the Target Macintosh.
For various reasons, some users do not use Time Machine for backups, and are making periodic disk images for later use. In many cases people will do this with an external hard drive, but if you do not have an external drive and you do have another Mac available (the backup Mac), you can use the backup Mac as an external hard drive for this purpose. For this you will enable TDM on the Mac that you want to back up (the target Mac), and on the backup Mac, you will run Disk Utility and select the target Mac (i.e. it will be something like “xxxx.xx GB AAPL FireWire Target Media”). Then click on “New Image,” and choose a file name and location to store the image on the backup Mac. Note that you can store it to a NAS drive if your backup Mac doesn’t have room.
BootCamp. This will not work if you have a BootCamp partition on the target drive. In this case you can use Disk Utility to make images of your individual Apple HFS partition(s), and third-party tools such as WinClone to make bootable backups of the BootCamp partition.
Disk repair and troubleshooting
If your Mac’s startup disk is in need of repair, you will not be able to use Disk Utility to repair it even if the system on the drive is healthy enough to run the utility. Most users will boot from their installation DVD and run disk utility from there. If you don’t have an install DVD or have no DVD drive, then you can use TDM. In this case configure the target machine for TDM and connect it to a healthy Mac and run Disk Utility. Then use the “Repair Disk” option in the “First Aid” tab of the utility.
Apple has a page on their support site regarding disk maintenance: “Resolve startup issues and perform disk maintenance with Disk Utility and fsck” http://support.apple.com/kb/ts1417
Hard Drive upgrades
When you need to put a larger hard drive in your Mac, you can backup the original drive as described above, then replace the hard drive in the target Mac and boot it in Target Disk Mode, run Disk Utility again and restore the image to the new drive.
If you have a BootCamp partition you will want to backup the Apple partitions and BootCamp partitions separately as described above, and then restore the Apple partitions with Disk Utility. Then use WinClone to restore the BootCamp partition. WinClone will take care of creating a new bootable partition. You may need to reactivate Windows after this procedure since the new disk drive will have a different hardware ID.
Migrating to a new Mac
If you are moving to a new or different Macintosh, you can use the Migration Assistant to transfer any or all of your User files, applications, settings and other files to your new Mac. This saves time and reduces the chance of missing some needed Application files. Detailed instructions can be found on Apple’s support website here: http://support.apple.com/kb/HT4413
Installing alternate OS X versions
If your computer doesn’t meet the minimum hardware requirements for a particular version of OS X, you may be able to install the OS on the machine anyway using TDM. For example, you may be able to install OS X 10.5 (or 10.6, or 10.7) on a PowerPC (G4 or G5) Macintosh. To do this, enable TDM on the PowerPC Mac and connect it to an Intel based system. Then load the Installer on the Intel Mac and install the OS onto the TDM volume on the target Mac.
If you have set the Open Firmware password to (among other things) disable TDM, you can press the Command-Option-P-R key combination during startup and enter your Open Firmware password to continue. This will give you a prompt, at which you can type ‘target-mode’ to continue with TDM on the computer.
Some users may choose to encrypt their home directories to prevent unauthorized access using FileVault. In this case, you will need to enter the FileVault password to access those files when using TDM from another host.
“How to use and troubleshoot FireWire target disk mode” http://support.apple.com/kb/HT1661
Apple Target Disk Mode, TDM, IEEE1394, 1394, FireWire, System Repair, Backup, Restore
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