6 Replies Latest reply: Oct 17, 2012 11:04 PM by babowa
davidkazuhiro Level 1 (0 points)



I'm trying to set up a RAID1 array with two 2.0 TB HDDs on my iMac.


While setting up the RAID, my computere crashed. I rebooted, and it crashed while starting up saying there was a kernel panic. I turned off the HDD's and startup up without a problem. Once I turned on one of the HDD's though, my computer crashed again.


Here are the steps I took.


  1. Open brand new HDD's from box
  2. Turn on HDD A
  3. Plug in HDD A to USB
  4. Time machine prompts if it can use it for backups, I say no
  5. Repeat steps 2-4 for HDD B
  6. Open Disk Utility
  7. Select HDD A
  8. Click RAID
  9. Drag both HDDs into the list
  10. Click options
  11. Select 256K block size
  12. Check "Automatically rebuild RAID mirror sets"
  13. Click OK
  14. Click Create
  15. Computer crashed
  16. Hold power button down to turn off
  17. Press power button to turn on
  18. Computer crashes while starting up
  19. Hold power button down to turn off
  20. Turn off both HDDs
  21. Press power button to turn on
  22. Computer starts up without a problem
  23. Turn on one of the HDDs
  24. Computer crashes after about 20 seconds


Any idea why this is happening? What should I do?


Computer Specs

iMac (27-inch, Mid 2011)

Mac OS X

Version 10.7.4

2.7 GHz Intel Core i5

15 GB 1333 MHz DDR3


External HDD specs (both are identical)

Model: Buffalo HD-EB2.0TU2J

Interface: USB 2.0

Data Transfer Rate: 480 Mbps

Supported OS: Mac OS 10.4+ (and Windows but that's irrelevant)

iMac, Mac OS X (10.7.4)
  • Radiation Mac Level 5 (4,645 points)

    Which brand and model of external hard drives are you using?



    Hope this helps

  • davidkazuhiro Level 1 (0 points)

    Thanks Radiation Mac


    As posted above, I am using two of the following in my RAID

    Buffalo HD-EB2.0TU2J


    Does that clarify the issue?




  • nurho Level 1 (15 points)



    I am not sure why they are crashing the computer, but you definiately want to be careful with an external RAID 1.  Here is what I would try first in your scenerio:


    1. Reset the drives somehow.  Obviously you can't do this on the iMac, maybe by formating them one at a time on a PC.

    2. Plug these drives in through a USB hub (possibily even a powered hub) since you can't connect the drives through each other.  Then before you connect the hub to the mac, you should have the drives fully spun up (in manual power mode, switch on the back) and the hub and on before connecting it to the Mac.  This way, both drives have a higher chance of appearing simulteanously to the Mac reducing any need for rebuilding because of out-of-sync issues.

    3. I'd then follow the steps in this article to reformat the drives for your iMac again:



    I've never attemepted a RAID 1 on external drives so you'd have to let me know how this goes.


    If all else fails, you could jump in on an order the school makes with the following company and get an enclosure to tranfer your drives into.  We have at least three of these enclosures at school, we are running one in RAID 1 and the other two in a RAID 0 configuration.




  • nurho Level 1 (15 points)



    Also, if you want to see where it is freezing on start up, you may want to hold "command-v".  More information can be found here: http://support.apple.com/kb/HT1492



  • davidkazuhiro Level 1 (0 points)

    I finally found the time to do a zero wipe on both drives.


    I'd actually used the exact same guide on my frist attempt, but had skipped the initial zero wipe part.


    Unfortunately, I ended up with the same results... during the RAID 1 configuration, the OS crashed, and the drives would crash the OS whenever they were plugged in after that. I had to format them with a PC to fix them so that they wouldn't crash the iMac again. Who knew.


    So I guess the iMac IS NOT able to handle a 2TB RAID1 configuration, even though it seems to think it can.


    I guess we'll have to give up and either buy an enclosure or just use one of them as a Time Machine backup drive

  • babowa Level 7 (29,955 points)

    Let me preface saying that I know nothing about a RAID setup; however....


    there is one thing that caught my attention - may just be a typo (and have nothing to do with your problem), but I thought I'd ask:


    Your original post says that you are running 15 GB RAM? That is an odd number, as the modules are supposed to match horizontally. Did you mean 16 GB?