doc/forum/correct_way_to_add_two_preexisting_datasets.mdwn

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+I've been syncronizing my data since long time, mainly using rsync or unison. Thus I had two 3.5Gb datasets set1 (usb drive, hfs+ partition) and set2 (hdd, ext4 ubuntu 13.04 box) which differed only in 50Mb (new on set1 ). This was double checked using diff -r before doing anything.
+I created a git annex repo in direct mode for set2 from command line, and after that I let the assistant scan it.
+After that created the repo for set1 and added it to the assistant. I think here comes my mistake (I think).
+Instead of keeping them apart, at told assistant to sync with set2.
+Why I think this was a mistake? Because set2 was indexed and set1 no, and I'm seeing a lot of file moving a copying, which in my humble opinion should not happen.
+What I expected it only the difference to be transferred from set1 to set2.
+What it seems to be doing is moving away all content in set1, and copying it back from set2. I think it will end correctly, but with a lot of unnecessary and risky operations.
+I think I should have independently added both datasets, let them be scanned and then connect to each other.
+So, now the questions:
+1. Is that the correct way to proceed?
+2. What if I have to identical files with different modifying times, I hope they are not synced, right?
+3. Is it posssible to achieve this behaviour of copying only the 50Mb?
+
+Thanks in advance and keep up the good work.
+Best regards,
+             Juan