Hello Mark Knoppix appears to show sda as a 2TB disk partitioned using GPT which will install a GPT partition immediately after the space normally used by the DOS MBR to provide more space for information about multiple main partitions, not just the maximum of 4 physical partitions in the old MS-DOS. Most computers search for the MBR, so it is used to re-direct the BIOS to the GPT partition. The main boot sequence is then controlled from the GPT partition, and none of the other partitions will be labelled as bootable. I often see some unallocated space at either end of the disc space, usually less than 1 sector, but most of sda appears to be a single partition, possibly using a swap file instead of a swap partition. Perhaps the disc was re-partitioned as a GPT disc, which would overwrite the original MS-DOS system, but then just left not further partitioned or formatted. There appears to be more information about sdb and its partitions without mention of corruption. If sda is corrupted do not try to alter it. There was a package "photorec" designed to recover deleted photos which was later enhanced to recover almost anything and may be re-named "testdisk". It is not a quick and easy recovery, but can examine, list, recover, and copy as many directories and files as possible to another formatted disc.
-- Chris Bell -- GLLUG mailing list GLLUG@mailman.lug.org.uk https://mailman.lug.org.uk/mailman/listinfo/gllug