The Case for Partitioning Your Mac’s Hard Drive


I’ve been partitioning my hard drives since my very first Mac — a used Mac Plus back in 1992. Yes, I divided the Plus’s commodious 20MB external SCSI HD into two partitions so I could boot either System 6 (for speed) or System 7 (for Internet support).

I’m not as big an aficionado of partitioning as I once was, although all of my Macs since the Plus have had partitioned hard drives, including the unibody MacBook I’m typing this on, which has two HD partitions. That’s down from the four or five I used to configure back in the days of PowerBooks and OS 9.

Reasons to Partition

Partitioning means formatting the hard drive with two or more virtual volumes, which appear on your Desktop and function as if they were separate drives. I have a number of reasons for using multiple partitions.

  • I like to be at least potentially able to install two different bootable operating systems on the same Mac — for instance, I have both OS X 10.5.8 Leopard and OS X 10.4.11 Tiger installed on my old G4 PowerBook (plus OS 9.2 to support Classic Mode in Tiger). Installing multiple boot systems makes version upgrades less of a dice-roll or leap of faith. Retaining a known-reliable older system installed is good insurance against disrupted work flow if the upgrade doesn’t go as smoothly as hoped. Also you may have favorite apps that aren’t supported by the latest OS version, of do a lot of testing of beta and/or alpha software, which has the potential to bollix things up.
  • Troubleshooting is easier if you have two bootable partitions. For instance, you can usually run diagnostic and repair utilities from one partition on another, which goes much faster than booting from a CD or DVD, and diagnostically if a problem goes away when booted from a different system install, it’s more likely a software issue.
  • By dividing up critical data, there’s less likelihood of catastrophic data loss due to file corruption. For example, a partition used strictly for document storage is unlikely to be affected by a serious system crash. Also if you have files that you want sharable without hassle among multiple users or across a network, you can create a partition volume for them with “Group” and/or “Others” read or read and write access.
  • Partitioned drives make it easier to find particular files if you always store certain types of files on particular volumes.

Boot Camp Requires Partitioning

  • If you’re running Boot Camp or one of the third-party virtualization solutions for Windows support, having Windows installed on a separate drive partition is a tidier way to proceed. In fact, Apple’s Boot Camp obliges you to have two (but no more) partitions. Boot Camp Assistant (OS X 10.5 Leopard and newer) automatically creates a discrete FAT 32, NT, or NTFS formatted Windows partition, but an important caveat is that Boot Camp Assistant doesn’t work on already partitioned disks, so with Boot Camp you’re limited to two partitions.
  • Since OS X supports both the Apple HFS+ file system and the standard Unix UFS file system, creating a UFS-based partition will allow the drive to be accessed by Unix systems over a network.

Downsides to Partitioning

Some folks tout using a partition for file backups, a practice I’m less enthusiastic about as it will be no help if the hard drive itself fails.

Other potential disadvantages of partitioning are that as smaller volumes fill up, fragmentation can increase, there will be less free space for swap files when running applications that depend a lot on virtual memory, and partitioned drives are more complex to restore after serious crashes.

As I mentioned above, while I still partition, I don’t go as ape with it as I used to, partly because there are fewer advantages to multiple partitions with OS X’s excellent support for multiple users and today’s drive formatting schemes than there were back in Classic Mac OS and HFS formatting days, and partly because hard drives are so much bigger and faster than they used to be (plus there’s the two-partition Boot Camp limitation, if that applies).

The most convenient time to partition your hard drive is when you first set up the Mac, although these days you can partition and change partition sizes without erasing and re-initializing the drive using OS X Disk Utility or third-party partitioning software like Prosoft Engineering’s $99 Drive Genius 2 or Coriolis System’s $44.95 iPartition.

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