Massive performance degradation on sustained sequential write
Solution 1:
The control disk is connected to a SATA port built into the motherboard.
As stated, the disks experiencing the journal flush time out issues are connected to the PERC, the same controller that the 'problematic' Toshiba's are connected to.
The PERC 310 is only a basic hardware raid card. It's CPU is probably easily overwhelmed, either that or there is a firmware bug. Direct AHCI is not a very common usage.
I would suggest the IO is locking up on the PERC, and not the OS