Percival P. Cassidy wrote:

The different failure rates for the Seagate ST4000DM000 and ST4000DX000
are interesting.

There's a significant difference in average age between Backblaze's DM
and DX drives. It looks like they've got a dwindling number of older DX
drives, clearly reaching end of life, and a huge number of younger DMs.
As the DMs approach the age of their remaining DXs, their failure rate
should rise.