[MacDV] Disk Fragmentation > Reformatting Single Partitions

[Michael Winter]

On Tuesday, April 15, 2003, at 02:54  PM, Illovox Media wrote:

> Please share your process for doing that.  I have wanted to be able to 
> do
> that for years, and do not know how.  Any reformat I know destroys
> everything on all partitions...

Sorry I took so long to respond, but since several people were telling 
me that they didn't think it would work, I decided I'd better be sure, 
so I hooked up an old 10 GB drive (USB) and went through all the steps 
to be sure. Here's how it works in OS X:

Open up "Disk Utility" and select the "Erase" tab. Two things to note. 
First, the list of drives in the pane alone the left. It will list each 
physical device and just below, indented slightly, will be the list of 
Volumes (partitions) on that device. So my device shows up as :

9.44 GB IBM -
      Music
      Photos

So you can see its a 10 (9.44) GB device with two Volumes (partitions) 
labeled "Music" and "Photos".

The second point to note is the warnings in the main panel. The first 
bullet point is:

"Erasing a disk results in all volumes of that disk being erased and 
one large volume being created on that disk."

The second bullet point is :

"Erasing a volume results in a clean volume being created."

Note the distinction between erasing a disk and a volume (partition).

So I selected the disk (the line that says 9.44 GB IBM-) and clicked 
the erase button. A warning dialog titled "Erase Disk" pops up saying 
"Erasing a disk will destroy all information on all of the volumes of 
the disk..." I hit the Erase button in the dialog box and a minute 
later everything on the drive is gone and I have one volume with the 
name "Untitled".

At this point, I went back and repartitioned the drive the way it was, 
copied a couple mp3's to the Music partition and a couple photos to the 
Photo partition, then went back the the Erase tab in Disk Utiltiy.

This time, instead of selecting the device (9.44 GB IBM-), I select the 
volume "Photos" and clicked erase. This time the warning dialog is 
titled "Erase Volume" (note difference) and says, "Erasing a volume 
will destroy all information on the volume. It will not erase 
information on other volumes on the same disk...". So again, I click 
the Erase button. The result is that I still have two partitions, just 
as before, but the Photos partition is empty, and the Music partition 
still has the mp3's I copied in.

So the short answer is that if you only want to erase a single volume, 
you select just that volume in the left pane before you click the erase 
button. If you select the drive, you will erase the entire drive. If 
you select a partition, you will erase only that partition.

Just a couple more notes. I hope hope nobody is confused by my using 
the words device and drive to mean the same thing, or my using 
partition and volume to mean the same thing in the above discussion. 
Also, though my test subject was a USB drive, I've done this with 
internal drives as well as external Firewire and SCSI drives. In fact, 
until this discussion came up, I didn't know you could erase an entire 
multi-partition drive with the "Erase" command. I thought you had to do 
it one partition at a time (which you do if you want to maintain the 
structure).

Hope this is helpful and not too long.

-Mike