The current set of G10 Ceph servers (karel, wumpus, and stobar) was acquired in 2018. Each server has 64GB of RAM, an 8-core AMD EPYC processor, 12 4TB hard drives, and two 400GB SSDs. See here for more info on how they are configured.
Waitaha, Barrel, and Valdes make up the failover Ceph cluster. The OSD disks themselves are on the Apocalypse array.
The current Ceph servers were purchased in the summer of 2018 along with Overlord, Torch, and Waverider (see 2018 Server Purchases).
After the events of the Cephpocalypse, karel, wumpus, and stobar became the new Ceph cluster. For a period of time, wumpus was running Ubuntu 16.04 LTS, leading to high latencies on the entire cluster. The ability to take it down (in the middle of a school day) to upgrade it (to 18.04 LTS with a newer kernel) is a testament to the fault-tolerancy and redundancy of Ceph.