2nd drive - Use for Mirror or Time Machine?

Discussion in 'macOS' started by lokiju, Sep 13, 2011.

  1. lokiju macrumors 6502

    Jun 10, 2008
    I feel a little silly for just now thinking about this but here's my story and I wanted to know if I'm missing anything.

    For the past 2 years I've been using my Mac Mini 2009 2.0Ghz model with it's internal 120GB drive as my main always on home server and media streaming device.

    I've attached to it a Sans Digital TowerRAID 4 bay SATA USB 2.0 enclosure. In that enclosure I've had four 1TB drives. The enclosure is only capable of doing JBOD (just a bunch of disk) so to OS X, it sees each disk in each bay as it's own disk. I've then been using Disk Utility and making two RAID 1 Mirror sets.

    Since one of my 1TB drives died in the enclosure, I bought two external 3TB drives that I confirmed beforehand could be opened up and the SATA drives extracted with ease. I did so and discovered that my external 4 bay enclosure only supports up to 2TB per disk after the fact. That said, I put the 3TB drives back into their enclosures and was starting the process of setting up a new RAID 1 mirror with the two 3TB external drives when the thought hit me that it'd probably be easier, safer and all around better if I just took the two drives and made one the active drive with the "live" data on it and the other only for Time Machine backups of the "live" drive.

    This "should" let me get point in time recovery on top of being a backup of my data.

    Is there anything I'm missing that would make this less ideal to do than the Mirror I've been doing up to this point?

    I confess I'm inexperienced with Time Machine and realize there might be something about it that I'm not aware of that would make this a bad idea.
  2. r0k macrumors 68040


    Mar 3, 2008
    Five words in your post stand out. I'm experienced *with Time Machine and having lost all my data about 7/8 of the time, I can say: Don't depend on Time Machine for anything other than daily backups. Don't waste an entire drive on Time Machine.

    * A wise friend once told me, "Experience is what you are getting when you think you are getting something else."

    Here are a few of the bumps in the road I've hit...

    My first gen Time Capsule died, taking 4 computers' backups with it. One of those computers experienced a drive failure while my TC was off at Apple getting repaired. The data is now gone. Forever.

    On 5 separate occasions, I have had to delete my TM backups and start over. The "sparsebundle" file became corrupted and I decided to wipe it and start over. In these 5 cases, I didn't lose anything except "old versions" of files that would have been available if I didn't have to wipe the sparsebundle file and start over.

    My wife's HDD partition table got wiped during a Lion upgrade. Unfortunately I didn't think to run any disk recovery programs and assumed the TM to TC backup would work as a restore point. I was wrong. I was facing the "corrupted sparsebundle" issue a 6th time only this time her data was gone. Forever. Well not quite. This time I also had crashplan. A quick trip to crashplan and I brought everything back.

    Now that I've talked about 7 disasters, I should in all fairness talk about one success. When I upgraded the HDD in my Macbook, I started a "fresh" TM backup to an attached firewire drive (not over the network!) I was then able to restore from that backup after installing the new drive. Since then I've turned to CarbonCopyCloner to do HDD upgrades but I want to be fair and admit Time Machine worked. 1 success out of 8 attempts. To me Time Machine is a convenience, not a backup solution. I should also be fair and mention that every failed TM incident occurred when backing up wirelessly. When I back up via ethernet, USB or firewire, results have been better.

    So to return to your issue, you could actually get away with both approaches. If you set up your 3TB unit in a RAID configuration, you can put regular data on the same drive you are using for Time Machine. There are a few caveats. Turn OFF spotlight indexing of that drive if you want "same day service" from Time Machine. You can then use crashplan (free) to back up to the same partition you are using as a TM backup or crashplan (paid, as I did) to back up to the cloud. But whatever you do, don't rely only on Time Machine for a backup.

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