If you loose your FT sets, because you used an old ERD or reinstalled, you should use the diskette created by Disk Administrator / Partition / Configuration / Save to do a Partition / Configuration / Restore.
If you don't have this backup, and don't have a tape backup, you may be able to use FTedit.exe to recover.
Disk Administrator creates data about your hard drives and FT sets at:
The information about each drive consists of the 32bit disk key, the start sector of the partition, length, drive letter, and wether it is a member of a FT set.
For each FT set, the type (mirror, stripe, volume set, etc.), number of members, and a pointer to the location in each partition is stored.
Only Disk Administrator can create this information, but FTedit.exe can manipulate it.