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Time Machine and Multiple Backup Questions
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slider
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Sep 5, 2012, 07:05 AM
 
Using Mountain Lion and I'm thinking about using the redundant Time Machine backup available in this OS.

The previous hard drive I used for TM backup since 2008 recently crashed. I've since replaced it with a new hard drive, but I've essentially lost 3-4 years of backed up data. I've only gone back to really old files a handful of times, and it was never for anything critical, but I liked that if I went looking for something that I thought/knew I once had on my machine that I could go back and attempt to retrieve it, but I digress.

I've searched around and generally know how TM goes about backing up to more than one drive, i.e. alternating, availability, etc., but what I didn't see leads me to my first question: When using more than one drive, does TM do an initial full backup on each new disk? I assume it does, otherwise having a redundant backup drive incase the other fails (i.e. if only one had the full backup) would be kinda stupid. But before I shell out more $$$ for another external hard drive I'd like this confirmed.

My second question is about making a backup of a backup hard drive. When my previous hard drive was failing and my new drive arrived, I attempted to move the old backup file to the new backup hard drive, but I ran into a bunch of permission issues and I wasn't able to figure out how to get around this. In the event that one of my two TM hard drives fails in the future, then the other drive would be the only one that had the really old stuff and if that ever failed it's just gone. If that happened, how would I get around the permissions issues so that I could transfer the backup to another drive? And, could I put it on the second new drive without screwing up future backups with it (or would it have to be a partition or separate partition or hard drive all together)? I've used CCC in the past to close a hard drive, would this be the best way to make a backup or a backup incase one of the two backup hard drives failed? Hope that wasn't too confusing.
     
OreoCookie
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Sep 5, 2012, 07:12 AM
 
Since you use Mountain Lion, I advise you to do something else: just configure Time Machine to use two Time Machine drives. Essentially you make Time Machine backups independently to two drives which gives you more data safety than your proposed 1 Time Machine drive + clone proposal (if you Time Machine drive goes bad and you clone the bad drive, you've just hosed all of your backups).
I don't suffer from insanity, I enjoy every minute of it.
     
slider  (op)
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Sep 5, 2012, 07:32 AM
 
Thanks OreoCookie,

Yes, my intention is to use two external hard drives to backup my data, both using Time Machine. My first questions was: Does Time Machine do an initial full backup to the second drive also? Again, you're response leads me to believe that it does in fact make a full initial backup on all new drives.

The clone drive scenario was in the event that one of my two Time Machine backups failed (say TM-1) thereby leaving the oldest data on only one drive (say TM-2). If the hard drive TM-2 then failed, the oldest data would be lost, so my second question was about backing up the oldest data on TM-2, either on the replacement drive for TM-1 (say TM-1R) as a partition, or on a third drive that cloned TM-2.
     
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Sep 7, 2012, 11:12 AM
 
I got a second external hard drive and have set it up with Time Machine.

Just to tie off my first question above, I can confirm that Time Machine puts a full initial backup on each additional drive attached (again, probably obvious, but so often the obvious is not always so).

In retrospect, given the cash I shelled out for these two drives, I might have been better off ordering a Raid (Mirror) since both drives are in the same location. In the future I may purchase a Raid and use one of my two external hard drives as a third backup that I plug-in periodically and store offsite.

As for my second question above: While I was considering my options, I came across a review where someone mentioned replacing your backup hard drive every three years. Once I read this it seemed obvious, since there are only two kinds of hard drives, those that have failed and those that are about to fail, it makes sense to be proactive about it. I don't know about the three year time period, I've not looked into the average life span of hard drives. My previous backup hard drive was actually a Raid 0 with two 750GB ATA hard drives which I purchased right around 4 years ago. So what I'll probably do is replace the drive when it is 36 months old and use CCC to transfer the data before attaching it. If one of the two drives fails before that, then I'll attempt to copy, clone, or just make a backup of the good hard drive so I have more than one copy of the oldest files. Of course things might be different in three years, but you gotta go with what you've got.
     
Spheric Harlot
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Sep 7, 2012, 11:48 AM
 
A mirrored RAID is not legitimate redundancy.

The problem is that crashes or failure are often preceded by little write errors.

If you don't have independent backups but simple duplication, you may have duplicated errors.
     
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Sep 7, 2012, 12:03 PM
 
Spheric Harlot - That's good to know, thanks.
     
BLAZE_MkIV
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Sep 7, 2012, 12:29 PM
 
Google has a really good study on lifetimes of hard drives.
     
   
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