Each Ceph cluster comprises a large number of individual storage drives that house both Ceph's internal metadata and the bulk data entrusted to us by users. By habit, many resources refer to these as disks, an artifact of the times when SSDs were not capacious or affordable, and even before they existed. Throughout this book we use the more expansive term drives to include other technologies. In practice and out in the community you will encounter the terms used interchangeably, though imprecisely.
Less capacious drive models are often attractive from a price/GB (or price/TB) angle than each generation's densest monsters, but there are other factors. Every drive needs a bay to live in and a controller / HBA / expander channel. Cheap drives are no bargain if you have to acquire, manage, rack, power, and cool double the number of servers in order to house them.
You may also find that the awesomeness of your Ceph cluster draws users and applications out of...