rsync repeatedly hangs during transfer

[Matthew DeNardo]

I have been using rsync to back up my desktop computer (Mac Mini, OSX 10.9.2, 2.5 GHz i5, 4 GB RAM) to a NAS (Dell Dimension running freenas 0.7.2 Sabanda revision 5266, Pentium D 2.66 GHz, 1 GB RAM). The Mac is connected to my router (Cisco E3200) via 5 GHz wireless G and the NAS is plugged in directly (the NAS has a 100 Mbps card). Until about three months ago, backups worked as expected. The transfers are in the Mac > NAS direction.

The command I am using is as follows: 
rsync -rvOltn --exclude '.DS_Store' --exclude '.com.apple.timemachine.supported' --delete /Volumes/Storage/Music/Albums/ 192.168.1.100::albums

Now, backups hang indefinitely at some point during the transfer. The only way to stop that is to Ctrl+C (^C) on the Mac and retry. Each time, rsync hangs in a different place or a different file. After a number of retries, I can usually get through an entire backup. Sometimes, the transfer hangs at 0% of the first file, sometimes during the first file, sometimes it doesn't hang until a number of files have been transferred (recent high streak is 22). Sometimes it even hangs on building the file list.

I have no clue what is wrong. I cannot recall changing anything configuration-related in that time frame. I pretty much had it set up and left it alone. I have not experienced any dropped packets that would indicate a network problem. Unlike the other thread on this list, the CPU on the NAS is NOT pegged at 100%; it's under 10% while the transfer is taking place and drops to 0% once it hangs.

Can anyone help diagnose the root cause of this problem and then, potentially suggest a solution? I've taken it as far as I can.


Thanks,
Matt