There are two reasons I want to partition this drive. One, Time Machine has no feature that allows you to bound the size of the backups. Therefore, it will keep adding incremental backups without removing older data until it runs out of room on whatever drive you are using. Considering I only have a 160 GB hard drive in my Macbook; wasting 1 TB of space is pointless, and partitioning a portion of the free space for Time Machine allows it to be “bounded.” Secondly, by partitioning the drive with two file formats, I can easily attach the drive to my network (via Airport Extreme, for example) and have it be accessible from all my computers. Therefore, simple Windows backups using SyncBack can be done using the same disk as no-touch backups using Apple’s Time Machine.

So how do you set up two partitions on an external USB drive– one for Time Machine and one for using with a Windows box?

0.) NOTE: FORMATTING PORTIONS OF HARD DRIVES WITH DATA WILL ERASE SAID DATA. IF YOU ARE A NOVICE AND HAVE DATA ON AN EXTERNAL HARD DRIVE YOU WOULD LIKE TO PRESERVE, I WOULD RECOMMEND MOVING IT TO ANOTHER LOCATION OR USING A DIFFERENT HARD DRIVE FOR THIS TUTORIAL!

1.) Plug your USB external hard drive into your Mac.

2.) Open Apple’s “Disk Utility” — this can be found in the Utilities folders within the Applications directory.

3.) On the left hand side, you will see the hard drive you wish to partition — you will likely see the manufacturer name (HD, not necessarily enclosure) — match the manufacturer and size. Select this drive (the top level, not any sublevels within the drive).

4.) Select the “Partition” tab on the top of the right side of the utility window.

5.) In the “Partition” tab select the number of partitions that you want from the ‘Volume Scheme’ drop-down menu. If you are planning on using a two-partition scheme like me (one for Mac, one for Windows), select “2 partitions.”

6.) Select one of the partitions by clicking on one of the “boxes” underneath the dropdown menu. They will likely be named “Untitled X.” When a partition is selected it will be bounded by a blue border and you will notice that both “Name” and “Format” are available.

7.) Start with your Mac (in my case, Time Machine) partition. Select a name, size, and choose either Mac OS Extended (Journaled) for a partition that you will use with Time Machine or use as a boot volume. Select Mac OS Extended (No Journaling) if you wish to use this partition for Mac media or data storage.

8.) Select the other partition by clicking on it. For a Windows partition, select “FAT” from the drop-down menu.* The name is not case-sensitive (i.e., must be in all CAPS) and cannot contain spaces. I typically will name this “WINEXT” or “WDWIN.” Something short and sweet in case you need to browse to it through a shell.

9.) Select each additional partition (if any) and then name and set the format.

10.) Click “Apply.”

Voila! You now have a drive that Time Machine can use for Macbook backups, but you also have a partition for media/data file storage on your other boxes as well!

*NOTE: Some people have e-mailed and asked “why FAT? NTFS is more awesomer!” Well, I agree that NTFS is the better file standard; however, as of 10.6.1, OS X still did not have the capability to write to NTFS drives; so FAT is the preferred solution here because it would allow you to write/edit the secondary partition from your Mac if needed.