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Thread: Partition a drive to GUID & APM?

  1. #1
    Join Date
    Feb 2012
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    Default Partition a drive to GUID & APM?

    I currently use a USB portable with 10.6, 10.7 and 10.8 on it and that works fine for most things I encounter, but recently I've been bumping into a few older Macs, particularly iMacs and the occasional Powerbook, that requires 10.5 on a firewire box. I had a firewire 2.5" box but that gave up the ghost a while back and I resorted to target mode on the G5 to do the necessary.
    But as I've just loaned out my G5 to a customer in trouble - dead logic board - taking my drive out and installing his mirrored set up, I went to put that drive into a USB/Firewire box that was sitting unused in a cupboard... only to find that it had a 1TB drive in it. That's overkill so I thought I could put it to far better use if I partition it into 4 and put the 10.6, 10.7 and 10.8 on it on GUID partitions AND put the stuff from the G5 onto an Apple Partition Map so it frees up the 750gb drive completely.
    To do that, of course, I need to be able to change the partition from GUID to APM... if it's even possible?

    I've been rooting through Drive Genius and taken a chunk out of an existing GUID drive to form a new partition but even that doesn't seem able to change a partition to APM.
    Any suggestions? Apart from using a separate drive altogether!
    The opposite of what you automatically assume to be the truth is the answer you're looking for!

  2. #2
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    Default

    A re-format doesn't do it?
    Damien,

  3. #3
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    Default

    No, A standard reformat gives you the opportunity to format as GUID or APM for the entire drive. You can then add as many partitions as you like, including as DOS etc, but that doesn't allow for a partition as APM as the only Mac option is for HFS+... or at least that's the only thing I've been able to do so far. If I set up a partition for Bootcamp it's going to end up NTFS so you'd think it would be possible to create a partition as APM if need be. I did think about seeing if I could set up a Linux partition and then reformat with rEFIT, but that doesn't give the option of APM either.
    Beginning to look like I've no option but to keep it on a separate drive
    The opposite of what you automatically assume to be the truth is the answer you're looking for!

  4. #4
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    It's my understanding that a drive has only one partition map, Apple or GUID and that shows the computer where the partitions are. Then each partition can be HFS or FAT or whatever format you want. In order to change the partition map you would have to format the entire drive as reformatting a single partition cannot change the partition map that contains it

    Disk Utility Would seem to confirm this as you can only change the PM when formatting a HD and not when formatting a volume contained on it

    This shows a limitation I was unaware of, you apparently can't have one drive capable of booting both a PPC and an Intel Mac due to low level HD formatting no matter what OS's you put on it. I bet that has caused people a lot more frustration than you have had I can just see someone screaming "WHY WON"T YOU WORK!"

    I don't think a single partition can't have its own partition map located within the drives global map. Even if it could you could still only boot from the computer that supported the global map because it would have to be read first

    Part of the issue here is that there is a difference between a volume format and a HD format. You can format a volume HFS+ or whatever but before you can even create a volume you have to have the HD formatted. The low level stuff like the PM and allocation block size (probably more) needs to be done first. There used to be a formatting tool that did these separately. First you formatted the HD and then it prompted you to create partitions
    Damien,

  5. #5
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    Agreed......that has been my experience anyway. If there is another way, I don't know it.
    "Imagine if every Thursday your shoes exploded if you tied them the usual way. This happens to us all the time with computers, and nobody thinks of complaining." -- Jef Raskin

  6. #6
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    Feb 2012
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    Having spent some time using every piece of software I could find before posting I was already at that conclusion... but the only stupid question is the one that doesn't get asked!

    Thanks for you assistance in confirming it.
    The opposite of what you automatically assume to be the truth is the answer you're looking for!

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