Quote Originally Posted by wpte View Post
I've transferred over 400GB already, but I did noticed some hiccups.
EXT4 seems to work well overall, good performance etc.
But after a while (seems almost random) I get a segmentation fault in cp, the drive becomes inaccessible and the router is not able to umount it, even when the drive is removed.
I don't see any oops, maybe I should turn extra debugging on?
The router is also not able to reboot after the segfault.
In case of you can't reboot, it seems to be kernel problem.
It can be either ext4(jbd2) specific or common writeback/bdi interfaces problem. I never hear that somebody did such stress-test on router, 400Gb is really huge amount of data!

Best of all, if you able to prepare reproducible minimal test-case.
If problem is ext4 specific, than switching to ext3 will help. To enable ext4 debugging you have to recompile ext4.ko, jbd2.ko kernel modules with CONFIG_EXT4_DEBUG=y & CONFIG_JBD2_DEBUG=y

Also, please try r4652 - it is a small chance that I miss something in latest backports.

Anyway, "cp" shouldn't crash silently - please try to use gdb to get type of fault.