Is it of any help if I run testdisk - Analyze on the other 3 disks as well?
Nope, it doesn't help at all.
Apparently, if I understood correctly, before proceeding with testdisk, the RAID needs to be mounted.
Yes, before you start any datarecovery using testdisk and datarecovery software also, your RAID must be mounted.
MS Data 1945734 17574131333 17572185600
ext4 blocksize=4096 Large_file Sparse_SB Backup_SB, 8996 GB / 8379 GiB
This partition ends after the disk limits. (start=1945734, size=17572185600, end=17574131333, disk end=5860533168)
Yes it looks like that your file system is ext4!
Doesn't this indicate that the original RAID-5 was ext4-fs with a size of 8.996GB, but due to a corrupted superblock at the beginning the system is not able to mount it as such?
Your RAID should be listetd with full size.
It means in TestDisk at the disk selection menu, you must select your RAID with full size.
The next menu would be partition table type and should be GPT.
The menu analyse displays your current partition table.
If testdisk finds your correct partition running Quick Search it will be displayed for recovery.
Each partition found by a superblok or its backup should be marked and you should press p on your keyboard to have a try to list your files.
If your files are listed, you can write this partition into your GUID partition table.
The menu Write will only write/register your found partition into your GUID partition table.
Now it's coming up the next!
If your superblock is damaged your partition would be available but appears as RAW (unformatted).
If your superblock is damaged you should run fsck.
But it's a little bit too early to judge as long as you have no RAID.
Typically message if you select only a 3TB disk is:
This partition ends after the disk limits. (start=1945734, size=17572185600, end=17574131333, disk end=5860533168)
I've seen some cases after a correct rebuilding of a degraded RAID and if the partition table, the boot sector or superblock and the file system were Ok, data were immediately available.
So datarecovery was not necessary.
Fiona