Resizing Partitions Dynamically on Mac OS X and other geeky stuff

If you’ve spent enough time around computers, you know the difference between disks and partitions. In a nutshell, disks are the physical devices that store data in a computer, while partitions are “logical” or “virtual” disks: a physical disk can, and often is, split into 2-3 or more partitions, making a single disk appear to be a bunch of smaller disks. Got it?

On the Windows side, there’s a great application that’s been on the shopping list of geeks and system administrators for years: PartitionMagic, but on the Macintosh side there’s never been a particularly strong entrant in this category.

I know, I know, you’re thinking: why on earth would I care? Why would anyone want to muck about with partitions anyway? Trust me, some of us need to do this sort of thing sometimes…

While working on a magazine article on installing Linux on the Macintosh, I reached a point where I needed to dynamically shrink the main disk partition on my PowerBook so I could create two new partitions, for the two different versions of Linux that work on the Apple hardware platform.

It was with some delight that I stumbled across VolumeWorks from SubRosaSoft, which promised to allow dynamic repartitioning of HFS+ partitions, the standard partition for a Mac OS X system. Just what the proverbial doctor ordered.

The theory was that I’d dynamically shrink down the partition, create two new, smaller partitions, then have space to install the new operating systems without having affected or altered the basic Mac OS X partition, operating system and all of my data files. That was the theory, at least. The reality proved to be somewhat more distressing, as the program froze during defragmenting the drive, then appeared to work properly when restarted, but the end result was that the newly shrunk partition didn’t have its block directory information properly tweaked. Subtract all the geek-talk and I’ve ended up with a dead computer that I am now reinstalling Mac OS X Panther on, from scratch.

Worse, I jumped the gun and installed one of the Linux systems available, but the Linux boot app that lets you choose between operating systems must be installed after Mac OS X is installed, so now I have to reinstall that operating system too!

Perhaps the most frustrating of all is that when I sent a problem report to SubRosaSoft about the situation, their response was “I suspect we may have a problem with FireWire Target mode. I will spend more time on it.” Indeed.

On the bright side, odds are good that the disk isn’t too badly fragmented since I had to reformat it before I began the clean installation of Mac OS X Panther. But that’s not much of a bright side after I’ve wasted about ten hours on this project so far…

10 comments on “Resizing Partitions Dynamically on Mac OS X and other geeky stuff

  1. Thanks for the warning re: VolumeWorks. I hate to say it, but the best partition software for Mac disks might be “MacDrive”, which runs on Windows. I’m looking around because Apple’s OS X Disk Utility is not heavy-duty. It ignores free space and also drops a lot of GB when setting up more than a half-dozen partitions. Also, the math gets ridiculous under certain circumstances, showing negative sizes (in bytes) for some volumes. (range error?). MacDrive can partition HFS+ drives from my PC and doesn’t lose any free space.

  2. A free way of repartition your drive is to boot from the OS cd, use disk utility to make an image to a firewire/usb drive, repartition, then restore your mac os x back to your drive.
    Ok, so I haven’t really tried it, but I heard it works and if anything goes wrong, you have the image and can restore to the full volume.
    Also, if you need mac os 9 stuff, partition with os 9 drivers then do not check the erase destination when restoring.

  3. You can definitely repartition your drive with the steps you outline, but it’s then a “destructive partitioning” and is basically what I was trying to avoid by dynamically repartitioning my system instead… 🙂

  4. By the way, fragmentation isn’t something you need to worry about in OS X because OS X includes on-the-fly defragmentation.

  5. I’ve heard good things about using parted (qtparted if you like the visuals) to dynamically resize a drive. I’m about to do it once I get the good-to-go from my roomate about risking destroying the drive.

  6. According to the Drive Genius 2 web site:
    Drive Genius 2 ($99) is able to repartition your hard drive ‘on-the-fly’ (no need to reformat the hard drive) allowing you to add, delete, hide or expand partitions live.

  7. Hi: but anyway what is (or what should be) the benefit of partitioning a hdd on mac os x?
    I mean, related to performance, not just file organization…

  8. I used SuperDuper to back-up my Apps disc, then reformatted and partitioned the Apps disc and restored the back-up using SuperDuper and now have Windows 7 and Mac OS on it.
    I’d used Bootcamp previously but with a clean disc it is easy to use the sliders to get different sized partions.

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