I'm transferring a large set of files from one disk to another using midnight commander (Telnet via Putty from a networked PC) and looking at my disk stats I'm getting big, consistent, more or less evenly spaced, drop offs during the transfer. I'm transferring large movie files that are more or less the same size which could explain the even spacing. Midnight commander is running the move in the "background" if it matters.

 

 

Is this normal behavior? Please see attached screenshot.

Assuming that there's nothing wrong in the syslog, its probably all because of the fact that reads of drives tend to be a lot faster than writes (especially once parity disks are involved).  So the system is reading the file (caching the writes), writing the file as it goes, but ultimately the write cache is going to fill up at which point its going to write what's in it and start the process again  Hence the regularly spaced slow-downs - when it has to dump the write cache to make room for more.

Thanks, just for completeness I've attached a screenshot where I moved to a 'foreground' midnight commander transfer. Looks a lot different!