Toshiba Hard Hard Drives
Toshiba is relatively smaller manufacturer by volume than Seagate or Western Digital whose main capability is with smaller format hard drives and storage devices such as Solid State Hard Drives. Fujitsu transferred ownership of their hard drives to Toshiba back in 1999.
Fujitsu Hard Drives and RAID Servers
Fujitsu transferred ownership of their hard drive manufacturing capability to Toshiba in 1999.
Seagate acquired Maxtor in 2006 and is a legacy brand of Seagate Technology.
Quantum was purchased by Maxtor back in 2000.
EMC purchased Iomega.
BackBlaze a data storage service provider, has undertaken a hard drive reliability study. They used an equal amount of drives from the top 3 manufacturers Hitachi, Seagate, and Western Digital and tested them in their environment. You can find reference to the study here.