Hey trurl !
Sorry for the long silence. I was away from home for a while. I thought i should replace all the SATA cables, before doing invalidslot just in case some of these errors were due to a connection issue. So last night, i replaced all cables, reseated the controller cards, left the new 6TB drive in disk1, fired up the server, mounted the disks, which mounted right away, and started rebuild the array. The rebuild has been running at over 100MB/s, no errors, and will finish in 17 hours. It is 97% done now. Woot !
Thanks again for your help trurl ! much appreciate it
I might just add a second parity drive for added redundancy and piece of mind.
Alex.