nouveau causes system freeze during periods of high disk activity

[lvm]

New install of 18.04 started to freeze when lots of files were being copied from one filesystem to another usually after several hundred gigabytes to a couple of terabytes: no messages, display freezes, no reaction to mouse, keyboard or network, the only way out is to powercylce the system. First I was copying from ext4 disk to a degraded md raid6, then, to isolate the problem, from one 10T ext4 disk to another 10T ext4 disk with the same result. Usually system froze so abruptly that there was nothing in syslog but finally some information was saved (attached) - probably partial as there was a block of corrupted data after it, and it pointed to nouveau. Replacing nouveau with proprietary nvidia 340.107 driver resolved the issue. Video is GeForce GT 240