Just out of curiosity, why do you span a RAID 1 over 2 partitions on the same physical harddrive?
Very good question because doing so would break RAID protection by artificially introducing a single point of failure.
That is not what I am doing, rather I have two RAID arrays, each spread across the same hard drives with each array occupying only 1 partition on each of those hard drives.
And in fact, the problem is now solved after taking a week to do offline btrfs backups which worked flawlessly, then after fixing the alignment problem and removing the dubious partitions they both mounted without issues, no data lost, making me really super impressed with btrfs tools. After five years without problems, finally when I do have a problem, the fix is straight foward and uneventful and no data lost.
As for the partitions created with diskdrake, I still don't know what went wrong with that but when the result is that multiple partition tools give different results as to a single partition, something is very wrong. So I deleted both the partitions with diskdrake and will now recreate them with gparted. The drive that failed the partitioning was a 1TB SSD, so I do wonder if the drive being an SSD could have had something to do with the partitioning fail.
The inability to mount the arrays was being caused by the alignment issue which probably had been around for a long time. The partition issue was a separate issue that was not preventing them from being mounted. I know that because in the case of one of these arrays I actually mounted the array after fixing the alignment problem and THEN removed the ghost partition (which had data from the array) and successfully retrieved all the array data back into the other drives in that array.
All of this has caused me to reassess my overall backup strategies because my backups in this case were on bluray discs and I had never equipped my second machine with a bluray drive making my backups useless. Added to that I found it impossible to find a bluray drive locally. Now, needless to say both machines have a bluray drive installed.
I also did not have an external drive to use in emergency which was a big fail on my part, and now I have one. With that on hand I decided to backup my second machine which operates with the whole root directory on one btrfs RAID 1 array spread over three SSDs and thats it. So I download Mageia 6 live disc and booted up on it to see if it would pass the test. First challenge, will Mageia 6 live be able to manage my btrfs array? Yup! No problem. Second challege, will Mageia 6 live be able to mount my external USB 3.0 ntfs drive? Amazingly no problem. I am VERY impressed with Mageia live disc! So I very successfully tarred the whole filesystem off of that pc, postgre sql and all onto the external drive just in case. I have been backing up the database regularly, but backing up the whole system will make things a lot easier in event of a catastrophic failure.