Keeping 2 external hard drives in sync

Discussion in 'Mac Basics and Help' started by Tulani, Jul 29, 2015.

  1. Tulani macrumors 6502a

    Tulani

    Joined:
    Dec 6, 2012
    #1
    Is there a way to keep two external drives in sync so that whatever changes you make on one automatically backs the same to the second such that if one fails you automatically have same copy and don't lose anything.
     
  2. 0d085d macrumors regular

    Joined:
    Apr 23, 2015
    #2
    It sounds like what you want is a simple RAID1 array.

    This "merges" two disks into one such that any data written to the combined disks is actually written to both disks. If one disk dies then you still have the data and can rebuild the RAID array when you replace the broken disk.

    Note that Time Machine is generally a better way to manage backups in the long run.
     
  3. Tulani thread starter macrumors 6502a

    Tulani

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    Dec 6, 2012
    #3
    I was of the impression that time machine only does back up of the Mac hard drive

    where as in this case I intend to sync just external drives with completely different content from the Mac
     
  4. 0d085d macrumors regular

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    Apr 23, 2015
    #4
    You can back up an external hard drive by going to System Preferences -> Time Machine, clicking Options... and removing the hard drive from the list of excludes. The hard drive has to be plugged in at the time.
     
  5. Tulani thread starter macrumors 6502a

    Tulani

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    Dec 6, 2012
    #5
    thank you, but the RAID 1 method seem to require to erase disk first whereas i was hoping to just sync what i already have on one to another
     
  6. Tulani thread starter macrumors 6502a

    Tulani

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    Dec 6, 2012
    #6
    i am also seeing some recommendation on some app called DropSync
     
  7. 0d085d macrumors regular

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    Apr 23, 2015
    #7
    Yes - you'd have to create the array and then put your data on to it. If you haven't got the spare storage to do that then this option isn't so feasible.

    I haven't heard of this myself, but from a very brief look it looks like it can probably do what you want.
     
  8. Gwendolini macrumors 6502

    Gwendolini

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    #9
    CarbonCopyCloner does this for some of my HDDs every hour, as I set it up to backup HDD1 to HDD2 every hour and so forth.
     
  9. MacUser2525 macrumors 68000

    MacUser2525

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    Location:
    Canada
    #11
    Or do it for free with already existing OS X tools. Open the Terminal.app then type in and hit enter key.

    Code:
    rsync -avP --dry-run --delete /Volumes/first_external_name/* /Volumes/second_external_name/
    
    
    This tells the rsync program to archive the data on the first drive to the second in verbose mode so you see what is going to do the P is there so if you control + c to stop it it picks up at the last point it stopped and does not start copying the last file it was partially through when interrupted from the start again. The --dry-run is just that a listing of what it will do no action taken (needs to be removed for actual backup to happen), the --delete will delete any files on the second which do not exist on the first drive giving you exact copy on both drives. The DropSync program is a GUI front end for rsync.
     
  10. Tulani thread starter macrumors 6502a

    Tulani

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    Dec 6, 2012
    #12
    thank you very much to all for the insights. i will try and go through them and find the best solution
     
  11. Fishrrman macrumors G3

    Joined:
    Feb 20, 2009
    #13
    I'm thinking Chronosync might be a good option, but I have no experience with it.

    Both CarbonCopyCloner and SuperDuper can create a "second copy" of the source drive that is functionally identical, but this is not an "automatic/continuous" process -- you either run the apps manually, or set up timed backups to do this.

    For example, you could run CCC two or three times a day, and your target will generally be "pretty close" to your original.
    This works well enough for me...
     
  12. prisstratton macrumors 6502

    prisstratton

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    Dec 20, 2011
    Location:
    Winnipeg
    #14
    I use rsync on my server to do exactly what you want and I schedule it to run automatically using Cronnix (free GUI front end to crontab editor).

    I found the following video very helpful:



    He starts talking about setting up the backup script at 4:30. He also explains how to setup Cronnix to automatically schedule your task.

    Cronnix, here:

    https://code.google.com/p/cronnix/
     
  13. LOLobo macrumors member

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    Nov 20, 2014
  14. Tulani thread starter macrumors 6502a

    Tulani

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    Dec 6, 2012
    #16
    wow......thanks. well illustrated.

    i am now stuck on which method to pick from everyones input
     
  15. Gwendolini macrumors 6502

    Gwendolini

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    #17
    You could also do it manually. Copy every file after file. Should keep you occupied.
     
  16. Tulani thread starter macrumors 6502a

    Tulani

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    Dec 6, 2012
    #18
    well said...but not too keen with an excess of 1 terabyte data
     
  17. Gwendolini macrumors 6502

    Gwendolini

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    #19
    Easy if you compress all the files to an .ace and copy that one file.

    But the rsync is the appropriate approach, CarbonCopyCloner just uses a nice GUI to do it for you.
     
  18. Tulani thread starter macrumors 6502a

    Tulani

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    Dec 6, 2012
    #20
    remember i also want to keep exact copy of any changes that happens on one seamlessly without me having to be too cognizant of it
     
  19. Gwendolini macrumors 6502

    Gwendolini

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    #21
    The compressing and manual labour was a joke.

    As to CarbonCopyCloner, some abbreviate it with CCC, it keeps copies of the changed files.
    My hourly backups of files I work on create a folder with the date of the backup in a separate folder , where the old files are put in the appropriate subfolders.

    Like

    HDD / Users / Tulani / Desktop / Work / More Work / file1 and HDD / Users / Tulani / Desktop / Work / Less Work / file2 are the originals you work on.

    When the backup proceeds and file 1 was changed, the old version from the backup goes to Backup HDD / CCC something / 201507311523 / Users / Tulani / Desktop / Work / More Work / file1.

    You don't need to backup the entire HDD though and you can backup to a backup folder of your liking on the target HDD. It is convenient and there is no hassle with scripts. I use it and I am not afraid of scripts, because I want to spend the time with more videos of whatever is in fashion.
     
  20. Tulani thread starter macrumors 6502a

    Tulani

    Joined:
    Dec 6, 2012
    #22
    just as feedback..........
    none of these solutions worked for me.
    i think something to do with my hard drives (Seagate and WD)
    i had taken the safest route by buying the dropsync app
    but the syncing did not go for long
    on close investigation i saw that even transferring files manually was triggering an error message "The operation can’t be completed because an unexpected error occurred (error code -50)"
    so i am doing one file at a time till i get the 1TB backed up sometimes even with failure because of this error
     
  21. Gwendolini macrumors 6502

    Gwendolini

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    #23
    What file system do the backup drives use? Mac OS Extended or Windows NT File System?
    Have you formatted them yourself with Disk Utility?

    I ask, as what you experience is not a normal behaviour.

    You could try some of the methods laid out here, especially the ones regarding sleep: https://discussions.apple.com/thread/4412045
     
  22. Tulani thread starter macrumors 6502a

    Tulani

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    Dec 6, 2012
    #24
    th
    thanks Gwen.......a bit frustrated for now
     
  23. mejosp macrumors newbie

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    Feb 14, 2017
    #25
    Can we re-open this subject please? I have same question. I do have time machine, but notice if my external is not hooked up to my laptop, time machine shows no entry for the HD. so my question to go along with this is that I thought time machine was to be used in case i lost / destroyed HD. But if time machine doesnt recognize the back up if it is not plugged in, what good is it if the HD is lost or destroyed?

    I also need to totally duplicate an external. Was thinking of using two externals and needing to have them both the same after every entry. How do I accomplish this?

    Or am i misunderstanding how the time machine works?
     

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