Rsync to-check grows during backup

Question

I am currently transferring about 40 Gigs of files from an external disk to my hard drive, and the rsync progress output always shows something like

... to-check=1100/24094)
... to-check=1099/24094)

But during the transfers, the second number grows, and the first never goes under 1000.

... to-check=1200/27199)
... to-check=1199/27199)

That leaves me puzzled - when will the transfer actually end?

Edit: Okay, at some point it ended. Still, what is causing that behavior?

Answer 1

rsync starts transferring the files before it finishes crawling to see exactly how many there are, to speed up the overall process. This means the number goes up as it's running.

As of rsync 3.1.0, this has changed a little:

The output of the --progress option has changed: the string "xfer" was shortened to "xfr", and the string "to-check" was shortened to "to-chk", both designed to make room for the (by default) wider display of file size numbers without making the total line-length longer. Also, when incremental recursion is enabled, the string "ir-chk" will be used instead of "to-chk" up until the incremental-recursion scan is done, letting you know that the value to check and the total value will still be increasing as new files are found.