>>105553891
4x4U dedicated to HDD storage space (but to be fair two of them are waiting to be upgraded from the almost decade old HDD pools in there), 3x4U GPU servers I upgrade whenever the used GPU market goes down in price significantly like a few years back when you could get 1080Ti's for basically nothing used, I got myself a tape library a while ago to manage offsite backups and 2x1U opnsense hosts for redundancy, the rest is mostly random old hosts slapped into whatever case I could get my hands on and an unholy mix of Cisco and Mikrotik network gear.
Originally my only real concern was being able to mount generous amounts of sound dampening panels in there and use low RPM fans because I had to keep the rack in my office back then.