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#11
Actually I decided to dump the whole idea of using Storage Spaces. After a bit more testing I discovered that I could replicate the problem in that the storage space did not work properly if the two external disks were started up in the wrong order.
If I repeated the actions in your post, then Storage space was fine till I re-booted.
I decided the benefits of Using Storage Space did not outweigh the hassle I was having. I had also bought a 4TB internal disk to help, and so I was able to change my plans completely.
Incidentally, both external disks passed Western Digital Extended Tests, and Crystal Disk Info tests so there should have been no issue from a reliability point of view.
Colin
PS I had first of all spoken to Microsoft 's help line and they told me there was nothing I could do and I'd have to format the disks. Luckily I knew enough to know that there was a solution somewhere if I could just find someone like you. Thanks again.