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I'm currently running Windows 7 x64 with a secondary data drive encrypted with Truecrypt. For the past 6 months or so I have been backing up the files on this drive manually to two other drives; using the 'overwrite older only' option in Teracopy for every conflict (as Teracopy won't let me set that option globally I have to do it manually for each conflict!), then a file analyser to manually find the files that have since been deleted on the source to delete them on the target.

I had a scare yesterday where the internal disk started clicking and then disappeared from Windows entirely. Fearing a failure I extracted the drive from my machine and placed it in my external USB caddy and it thankfully came up on my Arch laptop, then my Windows machine. In my panic I bit the bullet and installed SyncToy to automate this so I could sleep while it ran overnight. I used the 'echo' option and enabled the 'check file contents' for the first run to ensure it did it's job properly.

After completion, it appears that the new files have been moved across but the old files that existed on the target have not been deleted. I'm basically back in the same situation as Teracopy without a large amount of clicking, but still facing the prospect of manually analysing the drives with a duplicate finder.

As I use 2 externals in rotation as the target, is there some sync program for Windows that will smart-delete files on the target that don't exist on the source, while leaving existing unchanged files and adding new ones - with as little user input as possible? (I quite like this 'sleeping-while-it-works' idea)

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possible duplicate of Sync two external harddrives? – RedGrittyBrick Jan 5 '12 at 12:59
Note: Answer to Question referred to above, mentions tools which can delete files on target that are not on source. Answer applies to any mix of internal, external and remote drives. – RedGrittyBrick Jan 5 '12 at 13:01
Is there something about "ROBOCOPY /MIR source dest" that doesn't work in your case? – Goyuix Jan 5 '12 at 16:18

Thanks to a recommendation from here at superusers, I tested FreeFileSync I have worked with it for a while, and it is ok. See any of the bug reports there, incase your use would be different.

It can compare based on Just time and size , or do a full compare, then it Shows me what it is going to copy and destroy, then I can tell it to sync. There are all the usual necessary options, Like not deleting anything, backwards sync etc. A person can still potentially screw up their sync, select the wrong location, be in the wrong folder, or set it into the wrong direction. Being able to See mostly what is going to occur, and what is occurring, the general size and time via the GUI is useful.

EX: syncing up 2 different 2T drives to a 4T drive that has 2 partitions of 2T, so the sync is from 2T to 2T.

I am not sure about your 2 targets in rotation? If its just more disks to have to sync , then that is the same thing here. Myself If the target or the source partition doesn't match in size, or the folder itself, I will rearrange things so it does. For me it is important to quick viewing, and knowing what is going on, without a reliance on some extra tricks, that confuse it visually for myself also.

You can see in my example above, I could have put both drives to the one without partitioning, then I can't do a quick visual without math, I can't keep it simple. If the Original directory or partition is way larger than the external media, I would break it up into separate folders. As Human in charge I still need Quick visual size checks, quick visual compares, and if anything is acting strange, I can do side by side file exploring details.

For the solution to the terracopy not being able to do automated Damage :-) FastCopy will set that way by default. Sometimes it scares me :-) because set that way, hit the go button, and it isn't going to ask, just do.

I do not use TrueCrypt at all, so this post just left that all out, as if truecrypt is automatic and transparent :-) If it isn't , then that would be a big miss. TrueCrypt "Encryption is automatic, real-time (on-the-fly) and transparent".

That leaves this thought. My #1 rule of manual mirroring :-) and why I choose to manually mirror to begin with, as opposed to blind mirror. Never sync the drive when the other drive is having problems. Ever, no how, no way. Never trust File size only then , only a full compare, never delete anything then. If all the files had 2 bits screwed up in them because of a computer or hard problem, If all the files just had a new virus header added , or whatever other problem that can be directly cloned to the "backup" Instead of having 90% of your data , and missing the last few files, you could destroy your backup, and have nothing.

The Good fully alive backup should be preserved like gold, if the original hardware or disk is starting to act-up for any reason. The most recent data could be moved somewhere, even there, but not to push a full sync, especially not a blind sync.

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