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I used rsync to copy a large number of files, but my OS (Ubuntu) restarted unexpectedly.

After reboot, I ran rsync again, but from the output on the terminal, I found that rsync still copied those already copied before. But I heard that rsync is able to find differences between source and destination, and therefore to just copy the differences. So I wonder in my case if rsync can resume what was left last time?

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Yes, rsync won't copy again files that it's already copied. There are a few edge cases where its detection can fail. Did it copy all the already-copied files? What options did you use? What were the source and target filesystems? If you run rsync again after it's copied everything, does it copy again? –  Gilles Sep 16 '12 at 1:56
    
@Gilles: Thanks! (1) I think I saw rsync copied the same files again from its output on the terminal. (2) Options are same as in my other post, i.e. sudo rsync -azvv /home/path/folder1/ /home/path/folder2. (3) Source and target are both NTFS, buy source is an external HDD, and target is an internal HDD. (3) It is now running and hasn't finished yet. –  Tim Sep 16 '12 at 2:30
    
There is also the --partial flag to resume partially transferred files (useful for large files) –  jwbensley Sep 16 '12 at 16:15
    
@Gilles: What are some "edge cases where its detection can fail"? –  Tim Sep 19 '12 at 5:20
1  
@Tim Off the top of my head, there's at least clock skew, and differences in time resolution (a common issue with FAT filesystems which store times in 2-second increments, the --modify-window option helps with that). –  Gilles Sep 19 '12 at 9:25

2 Answers 2

i think you are forcibly calling the rsync and hence all data is getting downloaded when you recall it again. use --progress option to copy only those files which are not copied and --delete option to delete any files if already copied and now it does not exist in source folder...

rsync -avz --progress --delete -e /home/path/folder1/ /home/path/folder2

if you are using ssh to login to other system and copy the files,

rsync -avz --progress --delete -e "ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no" /home/path/folder1/ /home/path/folder2

let me know if there is any mistake in my understanding of this concept...

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Can you please edit your answer and explain what your special ssh call does, and why you advice to do it? –  Fabien Jun 14 '13 at 12:12

You may want to add the -P option to your command.

From the man page:

  -P     The -P option is equivalent to --partial --progress.   Its  pur-
         pose  is to make it much easier to specify these two options for
         a long transfer that may be interrupted.

So instead of:

sudo rsync -azvv /home/path/folder1/ /home/path/folder2

Do:

sudo rsync -azvvP /home/path/folder1/ /home/path/folder2

Of course, if you don't want the progress updates, you can just use --partial, i.e.:

sudo rsync --partial -azvv /home/path/folder1/ /home/path/folder2
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