BackBlaze was not alone (not sure who was first) to mount drives vertically. Xyratex did that in the near-line storage units (e.g. RS-4835), as did Hitachi and

BackBlaze was not alone (not sure who was first) to mount drives vertically. Xyratex did that in the near-line storage units (e.g. RS-4835), as did Hitachi and others. Once you've seen them, it's the obvious choice to maximize the number of 3.5" drives in a rack (~48drives in a 4U chassis). Heavy beasts though -- you want a lift to mount them. Don't know about relative reliability to horizontal mounts, but afair the drive manufacturer recommends mounting either vertical or horizontal and we didn't observe any obvious issues.