rsync takes a very long time to send file list

I'm trying to use rsync to backup some files from an internal harddisk to a usb-drive. (I'm working on a wd mybook world NAS)

There are two folders that I want to backup. A music folder and a video folder. The music folder(864 files, round about 10gb) worked perfectly in something about 1 hour (for the complete progress).

But the video folder(1025 files, round about 700gb) is still on "sending incremental file list" for now 8 hours. I don't think anything has been transferred. What could cause such a difference? The video folder hasn't that much more files in it. Yeah it is a lot bigger, but that shouldn't make a difference on generating the file list I think.

I'm using this rsync command:

/shares/extern # rsync -avPc --stats /shares/Public/Shared\ Videos /shares/extern/

I now since i am working on a NAS, I haven't that much cpu power, but it's far too long I think.

What do you think, is this behaviour normal? Are there any suggests what i can do to speed the whole thing a bit up?

I'm using rsync 3.0.2

The -c option forces rsync to calculate a checksum for all files. This means that it is reading the contents of all the video files before it starts deciding which ones to copy. That is obviously slow.

Consider removing that option if possible. You only need it in rare cases. See the description on the manual page for further details:

Note that rsync always verifies that each transferred file was correctly reconstructed on the receiving side by checking a whole-file checksum that is generated as the file is transferred, but that automatic after-the-transfer verification has nothing to do with this option’s before-the-transfer "Does this file need to be updated?" check.