Only thing I can think of is: have you used something like fdisk to format the underlying drives beforehand? I’ve seen comments on “low-level” partitioning causing some issues in the RAID setup. Unless you have already used them for storage, can you redo the setup (i.e. wipe the drives with low-level formatting, etc.)?
I have not experienced this problem in the past with a hardware RAID setup though…
I recreated the array splitting the RAID10 in two Raid1. Now the raid1 disks are seen completely (2.7TB net) and only one is still in two pieces (this was a raid1 even before). I’m not sure why but it’s good enough for what I need
I will also try to low format the partition still in pieces. Thanks for your feedback!