I had 3 of the 4 RAID 5 drives in my home server raid group go offline due to my PSU starting to die. I've replaced the PSU but now those drives do not show as part of the raid group, and I have not been able to find a way to add them back so I can recover the data.
The drives are fine and it was simply a case of plugging in/removing the drives during the identifying that the drives were fine and the psu was dead that seemed to do it.
The program freeraidrecovery.com gave the following information
This is a plain-text general description of the reconstructed array layout.
The array type is RAID5.
The array consists of 4 disks.
The disks are ordered as follows:
#00: Missing disk, to be reconstructed using RAID5 redundancy
#01: Disk 3 - WDC WD20EARS-00MVWB0, Serial number WMAZA4652359, \\.\PhysicalDrive3
#02: Disk 1 - WDC WD20EARX-00PASB0, Serial number WCAZAC873744, \\.\PhysicalDrive1
#03: Disk 2 - WDC WD20EARX-00PASB0, Serial number WCAZAC877534, \\.\PhysicalDrive2
Block size is 64.0 KB , same as 128 sectors.
The data starts at sector (LBA) 0 (this is often called "offset" or "start offset").
Array layout is Left (same as Backward), Asynchronous (same as Asymmetric or Checkerboard).
Parity starts at the rightmost column.
Generated by ReclaiMe Free RAID Recovery build 1204, www.FreeRaidRecovery.com
And screenshots of AMD RAIDXpert: