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What's the best way to keep two hard dives synced?

2758 Views 19 Replies Latest reply: May 10, 2011 8:49 PM by BobHarris RSS
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Doug_S Calculating status...
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May 4, 2011 7:37 PM

I've been looking at the best way to protect my data and I've learned a few things. My first thought was RAID but a bit more research showed RAID is not a fix-all. It has it's own problems and even if I use a RAID1 or RAID10 array (depending on the number of drives) a failure in one drive can actually set off another drive, killing multiple drives and still destroying my data. There are a few other issues I've seen, such as the way you need to manage a RAID system that don't overly appeal to me.


So what I'm thinking now is two separate hard drives that are synced in some manner. Both of these drives are going to be sitting on the back of my iMac at all times so there's no real worry about their needing to be connected to back up. The question is how best to do it?


So far my options are:


Chronosync: Software wise, I know this can sync across drives and as such has been something that interests me. However, I'm not sure how powerful it is and I'm still curious about how I would have to use it.


SuperDuper: Same thing as Chronosync, really, just a different piece of software.


Rsync: To be honest, this is the one that interests me the most. I need to look into it a bit more I'm starting to think this might be a great choice for me. With some caveats.


Basically, here are the things I'm going to use it for:


  • Two 3–4 TB HDDs or RAID0 arrays.
  • Storing of general project archives, images, documents, movies, music, that kind of thing.
  • Possibly for system backup with Time Machine.


Now, how I'd prefer it to work is:


  • I keep both hard drives plugged in via FireWire cables.
  • Ideally, whenever I edit, add or delete a file on one hard drive the change is immediately made to the other.
  • Once the syncing is set up I never touch it again, don't have to.
  • The only time I ever have to come back to it is if I'm swapping out one or both of the drives for larger ones.
  • All of this is controlled by some sort of GUI


I'm willing to accept terminal commands if I have to... But I'd really prefer not to. Also, if the syncing has to be done every hour or once a day or some other similar schedule I'm willing to accept that as well, though it's not preferred.


So that's what I'm looking at doing. I'd love to hear what you guys think.

iMac, Mac OS X (10.6.7), Intel Core i7 2.93Ghz / 12GB RAM / 1TB HDD / ATI 5750HD @ 1GB VR
  • Linc Davis Level 10 Level 10 (107,660 points)
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    May 4, 2011 8:10 PM (in response to Doug_S)

    I'd love to hear what you guys think.


    I think that what you're proposing to do isn't really a backup solution and shouldn't be confused with one. If all you want is redundancy in your storage devices, you'd be much better off with RAID level 1, which isn't a backup either. It's not clear why you don't like the idea of RAID. It will give you some protection from a drive failure. It will give you no protection at all from unwanted changes to files, and neither will your disk-synching idea, which is essentially the same thing implemented at the application level rather than the driver level.

  • Allan Eckert Level 8 Level 8 (39,370 points)
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    May 4, 2011 8:17 PM (in response to Doug_S)

    I tend to agree with your opinion of RAID and not Linc's. I think you are correct to avoid it. There are many pitfalls in setting it up properly.


    Personally what I do is to use both SuperDuper and TimeMachine. I feel that using both at the same time seems to get me good protection. I know I have been able to recover everything that I have had to so far.




  • ariefrommount barker Calculating status...
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    May 4, 2011 10:15 PM (in response to Doug_S)

    I use a 1 TB Time Capsule with Time Machine which does a backup very hour.

    I also use Super Duper with a 1 TB LaCie S+ARCK USB Desktop Hard Drive.


    I am glad I had both when my Time Capsule overheated and had to be replaced.

    Apple replaced it and transferred al of my information onto the new TC for free.

    The new TC gives me more information than before when backing up.


    This works fine for me.





  • kaz-k Level 4 Level 4 (1,995 points)
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    May 4, 2011 10:18 PM (in response to Doug_S)

    I'm using CCC, Carbon Copy Cloner to make bootable clone backup.

  • Stanley Horwitz Level 4 Level 4 (2,700 points)
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    May 4, 2011 11:48 PM (in response to Doug_S)

    Let me chime in for support of a RAID. I use a RAID and I am very happy with it. I use an older version of this and it has been running for at least a year without any problems. I use it as my Documents folder on my iMac. It is connected via Firewire 800. I also have a Drobo, but I use it only for Time Machine backups.

  • Stanley Horwitz Level 4 Level 4 (2,700 points)
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    May 5, 2011 3:47 AM (in response to Doug_S)



    As others have said, a RAID (or DROBO) as your primary storage is NOT a substitute for backing up your data. I bought my RAID array at least one year prior to my DROBO. At the time I bought my RAID array, 1TB drives were the largest capacity disks. I put two of them in and RAIDed them. Works great. Neither of those disks have failed.


    In my DROBO, I have two 1.5TB disks. One of those failed about six months ago. Replacing it was a smooth process, but the process to rebuild the data was slow (like around 30 hours ish) if I remember correctly. I use my DROBO for backups because it is the only way I can double the capacity of my RAID array affordably. I also find that the DROBO is a little too slow for my taste for use as a primary storage device. The rule of thumb for Time Machine is that your TM machine drive is at least as big as your primary storage. I don't quite meet that rule now because I also use my DROBO to back up my iMac's boot disk, in addition to my iMac's RAID array, but I also use it to back up my MacBook Pro via wi-fi. I like my DROBO because it offers me the ability to grow my storage easily. It has two vacant slots where I can pop in a pair of new disk drives. For backups, I don't much care that it is slow. A full backup of my RAID and iMac's boot drive takes three days, but it works. I am not a power user, but I suspect if I used it for primary storage, I would find it too slow.

  • BobHarris Level 6 Level 6 (12,505 points)
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    May 5, 2011 6:27 AM (in response to Doug_S)

    The best way to protect your data is to back it up using multiple Different methods.  That way a flaw in one methodology should not affect the others.


    SuperDuper or Carbon Copy Cloner are good choices for creating a full bootable clone.  They can also be used to backup to a networked file system (not bootable, but still a copy of your data).


    Time Machine is good for backing up your data on an hourly basis.


    If you have an off-site storage area (at least for critical data) that is also a very good idea as that protects against theft, fire, floods, huricanes, tornados, etc...


    If you are interested in rsync, then look more closely at Carbon Copy Cloner.  It actually uses rsync, and if you want to roll your own rsync, then at least get the copy of rsync inside of CCC, as it is the most Mac compatible up-to-date rsync.


    As for storage, as long as you have "Backup in Depth", then any collection of external disks is fine.  I've got Drobos, iomega, G-Drive, and a bunch of misc generic drive enclosures with commodity disks inside.  It is the "Backup in Depth" that counts, more than what you use as storage devices.

  • danegeld Level 2 Level 2 (180 points)
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    May 5, 2011 9:50 AM (in response to Doug_S)

    I very much agree with BobHarris: the most important thing is "Backup in Depth", that is, multiple backups in multiple locations. After experiencing catastrophic failure with RAID, I'll never use it again. Fortunately, at the point where it failed, I had one complete backup that was only about a week old, so overall loss wasn't horrible. I also don't trust software backup solutions, especially those that use proprietary file formats. Many years of storing and maintaining data has taught me (the hard way) that manual backups are the safest. I keep no data at all on my system drive, but only applications. That I do back up with SuperDuper and then check it for integrity. I also keep an external archive of application install DMGs along with their registration codes. As for data, I keep a minimum of four external drives for each type of data. Two are stored at home and the other two are stored separately off-site. I manually copy new and changed files to one drive and then replicate to the others. The process isn't automated at all, but it generally takes less than an hour each time I do it and I haven't lost any data in years.

  • kaz-k Level 4 Level 4 (1,995 points)
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    May 6, 2011 12:30 AM (in response to Doug_S)

    They'er, as well as 2T stuffs working fine as external and internal drives as far as I've been using.

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