Bus error with long running "cp" command

Question

I'm copying about 800Gb of data between a samba share and a local usb attached ext4 hard drive. I'm about halfway through, and I've noticed that after a couple of hours of copying any command that I run results in (for ls):

-bash: /bin/ls: No such file or directory
Bus error

This SO answer talks about the hardware being unable to address memory anymore, and this Quora answer also points out that the issue is related to memory being unavailable. However, there isn't any good advice on how to fix/avoid the issue, or whether it is symptomatic of a more broader underlying problem.

The first time it happened I rebooted the Pi in question and restarted the copy (with no-clobber -n switch), and the system went back to normal for a few hours. Now I'm getting the same issue again. Is anyone else experiencing this, and is there any advice for avoiding/fixing?

Edit

The Pi is attached to a 1.2A capable wall plug, external HDD is independently powered and is connected to the Pi by a powered USB hub.

• lenik: what's your power source for Raspi and local usb attached HDD ?
• Gerben: When copying large amounts of data I prefer to use rsync, as it can resume transfers, if something goes wrong. Not sure if this would fix your problem though.
• Krzysztof Adamski: anything strange in output of dmesg command?
• mrmagooey: @KrzysztofAdamski I'm not really familiar with dmesg, is there anything in particular I should look for? Nothing is jumping out at me, but does dmesg persist its messages across reboots?
• Krzysztof Adamski: @mrmagooey: We are looking for some network related errors, and something from CIFS filesystem or USB subsystem. Dmesg message does not persist across reboots.

Answer 1

The rpi can be iffy under high cpu load. use nice and rsync with a bandwidth limit. Update to the latest firmware. 15TB sync no problem.