https://serverfault.com/questions/13839/does-orientation-aff...
The easier answer I'm comfortable giving (despite me not being a sysadmin by trade) is that good storage software/setups should abstract over and protect you from something like this, because SSD/HDD bit-rot is absolutely a thing regardless of orientation -- if you're not using a WAL-ing (ex. zfs) or checksuming (ex. ceph's Bluestore) file system you're exposing yourself to data corruption. Only thing left is whether you'll actually have your drives long enough for them to exhibit complete failure from orientation, can't know that except to test like Backblaze/other providers do.
Makes sense to me, the parts are fixed, they're not heavy, gravity does not affect them.
However I've not seen anyone test this in real life.
FWIW I've only ever had drives mounted horizontally, the normal way and upside down. All of them had about the same lifespan.
For what it's worth, a bunch of server OEMs sell top-loading storage servers, eg. https://www.servethehome.com/dell-emc-poweredge-xe7100-100-d...
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.