ilanh Posted February 18, 2006 Report Share Posted February 18, 2006 I am backing up an internal HD from my PC to an external hard drive. It seems to me that duplication is easier than backup. Duplicate may create an identical hard drive on my external HD which can then be used in case of a crash. Am I correct in these assumptions? IH Link to comment Share on other sites More sharing options...
rhwalker Posted February 18, 2006 Report Share Posted February 18, 2006 Quote: Duplicate may create an identical hard drive on my external HD which can then be used in case of a crash. Am I correct in these assumptions? No, it doesn't create an "identical" hard drive unless you duplicate (or restore a backup of) a drive that is not currently being used. This has been extensively discussed here in the Retrospect forums: Is a Duplicate an exact duplicate? Can it be used in case of a crash? Perhaps and probably so. If the duplicate was done of a drive not currently being used (not the current boot drive), yes. If the duplicate was done of the currently active boot drive, perhaps and probably so. If the duplicate was done of a currently active Mac OS X Server boot drive with services (e.g., mail services) active, no. Again, see the previous discussion in the Retrospect forums. Basically, it's a problem with making a "duplicate/clone/copy" of a live booted disk, which is changing as the duplicate/clone/copy is being made. The only way I know of to make an "identical" copy of a live booted disk is to create a RAID 1 mirror and split the mirror once the two (or more) drives of the mirror have become in sync, but even that might not give a "valid" disk because it's hard to know the "correct" moment to split the RAID mirror if the system is live (unless you shut down services the moment before the RAID mirror split). For a quiet system, without stuff running in the background, or a disk that is not active, it's much simpler to make an identical duplicate/copy/clone. Regards, Russ Link to comment Share on other sites More sharing options...
ProfN Posted February 18, 2006 Report Share Posted February 18, 2006 Retrospect 6.x.x Duplicates of my boot volume have served me well on my non-server G4 and G5 when I've experienced hardware crashes or nasty corruption caused by my donated alpha and beta testing and I have to boot the Duplicate. I always run Compare as part of the Duplicate process to see what changes occur between two hard drives because of active processes. Respectfully, Norm Link to comment Share on other sites More sharing options...
CallMeDave Posted February 18, 2006 Report Share Posted February 18, 2006 Quote: It seems to me that duplication is easier than backup The are different processes, designed for different needs. Duplicate will result (withing the limitations suggested by Russ) in a Destination that has only the same files as the Source at the time of the most recent Execution. Backups will result in an ever growing set of changed files, with each version maintained during each Execution. Backups are better if you t need to go back to an earler version when the current version has been modifie or deleted. Duplicates are better if you want to have a Finder readable collection of files for fast access. Having just acquired a new Destination drive for backups of a personal/work machine, this is the scheme I've come up with to try for a while: - During the weekend, when the machine is unused for home-office duties, shutdown and rboot from uninvolved third volume. - Duplicate entire internal HD to external FW HD. - Reboot from internal HD. - Configure Retrospect with a scheduled Duplicate script: Source=/Users/my_home_directory/ (defined as a subvolume) Destination=/Volumes/My_External_HD/Users/my_home_directory/ (defined as a subvolume) Since the critical files on this machine are those that are contained in the home directory of the only active account, this will give me a machine that is guaranteed to boot (to the system status of the weekend Duplicate) containing the datafiles that were present at each Duplicate Execution. I'm much less concerend about possible changes to higher level directories (/Library, /System, etc) that might occur during the week (say changes in LittleSnitch configuration, or even changes to Retrospect's preference file). It also cuts _way_ down on the scan time for the Duplicate, since it doesn't need to look at the many thousands of files that live in those higher level system folders, nor does it need to scan/match those same files on the Destination volume. I can then repeat the full system backup during the weekends, if I care to. And note that this method is in addition to a File Backup Set of the home directory that's Recycled every few months (when the drive gets full). And the optical disk burns of projects and other files done (without Retrospect) on a regular basis. Hard drives fail; more backups are better. Now, I haven't actually _tried_ this setup yet. But it seems promising in my head. Dave Link to comment Share on other sites More sharing options...
ew02748 Posted February 19, 2006 Report Share Posted February 19, 2006 I do both to get the best of both worlds! Duplicate: Immediate access to duplicated files without retrospect software. Gives me a good feeling that I can see the actual files duplicated. Can restore to a borrowed computer temporarily while I fix my primary pc without installing retrospect. Comprehensive: Better because you can restore files that you accidently deleted and go back to earlier versions of files. Worse because you need retrospect to access the backup and because it is more black box to the user so you have to run with a little more faith that it is all working correctly. If you do both you get all the best of both. Link to comment Share on other sites More sharing options...
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