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.



In response to elektek…

Try Soft Raid software, I believe it is capable of doing what you request. Very good software by the way! You can check it out at their site. Just enter
Good luck


cheers, but just wiped it and started again :( I am having problems transferring my TM files to a new drive partition though – maybe someone can help me with this too?



Hi everyone,

I have a macbook and I have two external hard drives. I have partitioned both but only one of them will let me change the size of the partitions without having to reformat. Is there any way to alter the sizes of the partitions of the one that wont let me change using disk utility, without having to erase the information?


Is there any available source for testing results showing the benefits or disadvantages of partitioning? While I appreciate the recommendations of many people who use this system (and IU actually have two drives partitioned, myself), I would like to see evidence that there is factual proof from unbiased, scientific evaluations.

Maybe I’m just lucky, but I’ve never had any disk problems either with or without partitioning. But that has been with different hardware, OSs, etc. Hardly a confirmation that either method is better or worse. It’s simply MY experience. ;-)

Thanks! And here’s to NO one having any disk problems no matter WHAT they do!!! :-)

Dave Greenbaum

Great article.
For the first time since 1984, I didn’t repartition my new iMac. I wasn’t going to use multiple OSs on it. I now own 2 pc laptops and a Macbook and then a Mac Mini for testing.

My partitions were always the same:

Applications (merged that into System in OS X)

Scratch was used as a scratch drive for graphics apps and it would become highly fragmented and often corrupt. It allowed me to quickly erase it and, pardon the pun, start from scratch.

Having System on it’s own partition allowed upgrade without risk of the data getting overwritten.

Whenever I upgraded the OS, I’d always install it on Scratch, wait until it’s reliable, and then rename System Scratch and vice versa.

RichC in Nidderdale

Multiple partitions are possible with BootCamp.

I currently have 2x Leopard partitions and a Windows partition on my MBP15″ 320GB stock drive. If I remember rightly -from over a year ago- I just had to format the Mac OS partition (+ install 10.5), use BootCamp to create the Windows partition, resize the Mac OS partition which allowed me to make another partition, then finally edit the boot.ini in the Windows partition (change the Windows drive from drive 3 to drive 4). The XP partition works in BootCamp and in VMWare although it does take a little while longer to boot in BootCamp and I’m not sure why.

Honestly, I either did the above or I created the original Mac 10.5 partition the correct size (the size it is now) and left the rest as free space before using BootCamp to create the Windows partition then Drive Utility to create the 2nd MacOS partition. Finally I edited the boot.ini in Windows. My memory is not what it was!

Going to put 10.6 on one of the partitions over the holiday season – fingers crossed…


I have been partitioning for years (all the back to a 10MB Profile) – I have a system partition, a user (work) partition and a parallels partition on my probook and iMac (i7). I have found it easier to keep “crud” out of the system and have had fewer errors from this approach. It is also easier to update or change system, when personal data are on a separate partition. Backup is easier too and I can restore a partition without influencing the rest of the disc.

Having a 1TB hard disc with one partition can get complicated in a hurry.





Interesting article. I hadn’t thought of many of the benefits you mentioned here before. Can you please explain in more detail what you meant by this: “For example, a partition used strictly for document storage is unlikely to be affected by a serious system crash.”? How would my documents be any more secure if in a separate partition? Does a “serious system crash” overwrite data in my documents folder in one partition but not another? Thanks.


By creating 2 Partition only advantage you got is if you OS crash like mention in article “system crash” you can do a fresh install on that partition without having impact on 2nd partition.
Only thing need to be taken care in all software need to be install in system OS partition installed, otherwise if you do re-install and if your software are installed in other partition you will not be able use those software’s

Jon Henshaw

I like the idea of using multiple partitions, but I’m not going to go down that path until a file system as smart as ZFS appears on Mac OS X.

Baby Food Grinder

Good article. I think I’ll be partitioning my iMac soon as it’s been 2 years since I bought it and I’d like to do a clean Snow Leopard install. Partitioning will help me the next time I want to reinstall.

Denis Lemire

The last point about UFS filesystems setup on an alternate partition being accessible by UNIX systems over a network is misleading. When you share a filesystem over a network, the underlying filesystem is irrelevant as it is abstracted as NFS, CIFS or etc… The actual filesystem isn’t exposed over the network.

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