Using external HD to boot from

Discussion in 'iMac' started by applejacker, Oct 2, 2012.

  1. applejacker macrumors newbie

    Joined:
    Sep 23, 2012
    #1
    As per a previous threat I have been trying to help a friend with his iMac. Everything points to a HD issue. While I was troubleshooting I backed everything up with time machine on a 1TB external HD. (not a firewire 800 or anything)

    Is it possible for me to install the ox onto this external hd and use that as though it was his internal one instead of removing the possibly defective one?

    Thank you.
     
  2. simsaladimbamba

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  3. GGJstudios macrumors Westmere

    GGJstudios

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    May 16, 2008
    #3
    Yes, it is possible to boot from an external drive. Just hold the Option key down during startup to select from available boot drives.
     
  4. applejacker thread starter macrumors newbie

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    Sep 23, 2012
    #4
    Thank you very much for the quick replies.

    The hd I used for the time machine backup does not show up when I press the option key as there is no os on it right? I see it when in disk utility though.

    If I partition the external hd I used for his backup and install the os there will that work do you think. Sorry for my questions but I have never used a mac before.. now I want one of my own though lol
     
  5. GGJstudios macrumors Westmere

    GGJstudios

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    #5
    Right. TM doesn't make bootable backups. For that use Carbon Copy Cloner
     
  6. applejacker thread starter macrumors newbie

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    Sep 23, 2012
    #6
    I don't have access though to that because while troubleshooting I erased his hd. I am not able to reinstall the os on it so the only option on boot up is the reinstall cd. :(
     
  7. Weaselboy Moderator

    Weaselboy

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    #7
    Correct... no OS on the Time Machine backup so the iMac can't see it.

    You can start from the DVD then use Disk Utility to shrink down the Time Machine partition to make space for a second partition. Then add the second partition and install the OS to it. This will take quite a bit of time and when done will be very slow, but it will work and will allow access to data etc.
     
  8. applejacker thread starter macrumors newbie

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    Sep 23, 2012
    #8
    when you say it will be slow do you mean that is I was able to do this then it would be very slow for the guy to use on a daily basis? Would you suggest he bought the firewire 800 ext hd and I could install the os onto that. Would that allow him to use his imac at the regular speed?

    I really appreicate all your replies.
     
  9. Weaselboy Moderator

    Weaselboy

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    #9
    Yes, running the OS and all from an external USB drive is going to be painfully slow. A FW800 will be much better, but still not as fast as the direct SATA connection of the internal hard drive.

    You might try buying an inexpensive FW800 enclosure then swap in the 1TB drive you are now using and see if that gives you acceptable speeds. You can grab FW800 enclosures pretty cheap. It would worth the shot I think.
     
  10. applejacker thread starter macrumors newbie

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    Sep 23, 2012
    #10
    So you don't think a firewire 800 ext hd would be fast enough? The iMac is not used for gaming or anything, just regular surfing, storing photos, email and office suites etc.
     
  11. Weaselboy Moderator

    Weaselboy

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    #11
    For light usage like that I think it would work okay, but you will be able to tell the difference.
     
  12. applejacker thread starter macrumors newbie

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    Sep 23, 2012
    #12
    ok thanks, if it was a pc I would be ok swapping out the internal hd but looking the imac up on youtube it looks really tricky. I think you even need a special tool to remove that sticky tape from around the exterior. Someone mentioned today that it is common now to use ext. hd's as the primary boot so I feel dissapointed to hear it will be a lot slower lol

    Thanks again for your help.

    ----------

    I just noticed I typed "threat" instead of thread in my first post lol sorry about that lol
     
  13. Weaselboy Moderator

    Weaselboy

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    #13
    Just another thought... I have not tried this myself, but other forum members have installed an SSD in an external FW800 enclosure and been very happy with the results. Even though there are still limitations in gross data throughput, the greatly reduced latency (seek speeds) of a SSD more than make up for it in a usage case like you are describing. SSD prices have really come down, so this might be a good option if the storage needs are not large.

    I'm with you... it scares me to death prying the cover off an iMac. Lots of people here do it though.
     
  14. applejacker thread starter macrumors newbie

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    Sep 23, 2012
  15. excommie macrumors regular

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    May 12, 2009
    #15
    I booted my iMac (24 inch, 2.8Ghz Core2Due) from WD Caviar black on a FW800 drive. It was faster than running it on the stock internal drive. I ran this set-up for about a year, without a single crash.

    Recently I wanted to upgrade my internal drive to SSD. Before opening my iMac, I tried booting the SSD from the FW800 bus. It is so fast I never bothered opening the iMac. Moutain Lion boots in less than 20 seconds. All apps open in a single bounce (even MS Word & Excel open in a single bounce - these apps used to take forever to open when running on the internal drive).
     
  16. applejacker thread starter macrumors newbie

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    Sep 23, 2012
    #16
    Thank you excommie,

    That is interesting. I wonder why so many online say it will be slow. I will definitely look into this.
     
  17. excommie macrumors regular

    Joined:
    May 12, 2009
    #17
    Most online sites look at raw numbers. However none of these sites actually tried booting SSD from FW800 bus (Windows doesn't allow it, FW enclosure cost is also a factor).

    The truth is that any OS is a collection of small fragmented files. When loading these small fragmented files sequentially - the OS load does not saturate FW800 bus.

    The SSD drive on a fast bus would have a tremendous effect when opening LARGE files (ex. for video editing), but to load OS files and open applications - FW800 bus is doing just fine.

    If you read responses from people that actually tried doing it - they'll all agree with me. There is also a lot of naysayers - these people are just speculating.
     

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