5.1 hangs on large file transfers

["dd dd"]

HI Fellows,
sorry bothering you.
There is probably an inssue with 5.1-RELEASE.

I got 2 hdd attached to separate cables/controllers.
At the boot time I can see something like:

ad0: 9732MB <SAMSUNG SV1021H> [19774/16/63] at ata0-master UDMA100
ad2: 76351MB <SAMSUNG SV0802N> [155127/16/63] at ata1-master UDMA100
ad2: UDMA ICRC error cmd=read fsbn 0 of 0-3 retrying
last message repeated 2 times
ad2: UDMA ICRC error cmd=read fsbn 0 of 0-3 falling back to PIO mode
last message repeated 2 times

Then system runs and looks alive and kicky.

Buut when I'm trying to perform large file transfers from one disc to another, 
the system freezes with no diagnostics. Even when I press something like 
CapsLock led does not blink.

I read some posts concerning this issue. So, I turned off any NFSs and changed 
cables, stripped kernel to minimum functionality (however still running 
natd). Still got this problem.

When I do any transfers on the same hdd -- everything looks fine.

The same disks with 4.7 installed work with no problems.

Can this be motherboard/samsung incompatibility or just software tricks?

Thanks in advance,
Dmitry.

P.S. please reply to me directly cause I do not read the list.