Comment 1 for bug 784840

I wanted to say that I'm fairly sure I've figured out what is causing this problem. I have many large files on my system as I have a ton of VM images, ISOs, and other things. The huge increase in time only occurs when the 'Use checksum to detect changes' option is enabled (I think it was on by default).

I did a bit of research and rsync uses the MD4 hashing algorithm to compute these checksums. Unfortunately, checksums on large files can take a very, very long time. For instance, the xubuntu-11.04 iso (<1GB) tok nearly 30 seconds to compute (time openssl md4 /xubuntu-11.04-desktop-amd64.iso) and that is without nice or ionice enabled.

Turning off the checksum option causes BiT to function at a normal speed. Perhaps having the option off should be the default option and a warning should be placed next the the option?

Note: I am unable to explain why this worked fine before 11.04. Maybe a revision in rsync changed how the checksum was computed?