file corruption

[xiaolong mou]

Hi,

I am backing up about 500G of data from a linux-based NAS to a USB
hard drive attached to a router (rt-n16 with tomatousb firmware). Both
NAS and the router have rsync-3.0.9. The router is running rsync in
the daemon mode. To test the set up, I rsync'd the files to the empty
USB hard drive, then back to the NAS in a new temp dir. Afterwards, I
did a local "diff -r" on the NAS. To my surprise, a few files were
corrupted (only 3 out of 17K files). "cmp -l" shows single byte
difference between the original and rsync'd files. However, I didn't
see any error message on the NAS side or in the rsyncd logs. How is
that possible? Doesn't rsync always do a checksum verification after
copying the files?  I have been using rsync for years for local
backup. The feeling of silent file corruption is scary. Could someone
point me to the right direction? I really want to get to the bottom of
this. Much appreciated.

Regards,
Xiaolong