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I've got 2 GMax external drive enclosures, each one takes 2 3.5" SATA disks (up to 1TB per disk), configured to appear as a single 'JBOD' unit. I use FW800 out of the MacBook Pro into one unit, and then the pass-thru connector from that unit to the next one (each unit has a pass-thru connector; these boxes really were a steal at the price).

I use one unit as my main 'projects and laptop backups' drive, and the second unit is my backup copy of the first one. I've been managing the backup copies using SuperDuper!, manually initiating a 'smartcopy' of the main drive to the backup drive at least once a week.

The disks I had in one of the units recently failed, and now I've bought 4 identical new 1TB Seagate disks. Before I set things up much as they were before (2TB in each unit), I was wondering if I could make a software RAID 1 unit out of them? I thought that this would be an easier system for me to manage than manually backing-up.

Has anyone run a software RAID 1 drive on external drives like this? Is it worth the trouble, or should I stick to my current regime? I'm not looking to increase performance at all, I'm looking to minimise the human-involvement in my backup process. :-)

This would be on the current patch of Snow Leopard.

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  • I would have tagged this as Firewire-800 and RAID but I don't have the rep to make tags and we don't seem to have suitable tags created (yet!)
    – robsoft
    Commented Sep 7, 2010 at 10:57

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I haven't tried FW800 specifically but we use a lot of OSX-RAID1 on internal drives and i used it once on FW400.

You just have to create a mirrored disk set from the external disks in DiskUtility. You should use the whole disks and let DiskUtility do the partitioning. That makes it easier to rebuild and boot off the set.

You can also start out with data already on one disk, then create a degraded set on a second disk, copy everything over and integrate the first disk into the set but this requires some non-supported use of command-line diskutil. The same goes for creating partitions on the RAID set or creating a RAID out of partitions. (All of which is perfectly normal and handy on e.g. Linux)

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  • Working a treat, so far! I had the data already on one disk, so I used that enableRAID then rebuild approach. Thanks for your help!
    – robsoft
    Commented Sep 10, 2010 at 11:44
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A RAID setup is not a backup. A RAID is a way of mitigating hardware failure, its value is that despite a piece of hardware failing you can keep working with no down time. In your case, the issue you had a (a failed drive) would have been handled just fine by a RAID, but the following would not:

  1. Accidentally deleting a file (the RAID will happily delete it on both of the mirrored drives.
  2. Data corruption due to bugs in any programs you are using (again, the RAID will dutifully store the bad data the apps send to it).

The above are software and user failures. If you are confident you (or an app) will never make a mistake where you need to rollback to an older version then you simply don't need a backup, and going to a RAID to mitigate potential HW failure is fine. If you are like the rest of us an make mistakes then you probably want actual backups, and to add a RAID in addition to that if down time is very costly for you.

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  • Thanks Louis. I guess I didn't really explain the nature of the data on the drive to begin with - these are archives and backups of files on my laptop, not the 'originals' themselves. I'm not using the raid device instead of backup, I'm already using one JBOD to keep my backups on, and as an alternative to copying those backups to a second volume (backup of my backup), I want to use RAID to do that step for me. I appreciate the good advice though!
    – robsoft
    Commented Sep 7, 2010 at 12:34
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    In that case RAIDing them makes perfect sense. The one issue is that since they are separate external enclosures you want to be extra careful about plugging/unplugging them, as doing it willy-nilly could cause the raid to degrade. The setup you have seems like that is not a problem, but just make sure you are careful.
    – Louis Gerbarg
    Commented Sep 7, 2010 at 20:09
  • Thanks, I am going to have a go at the weekend. i also want to look at how I can organise the FW cables so that they are harder to snag/remove. :-)
    – robsoft
    Commented Sep 7, 2010 at 22:07

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