Most database performance problems are a working set that no longer fits in memory, or a commit that waits on a slow flush. How to measure both, how much RAM and what kind of disk to buy, where the CPU matters, and how to lay out replicas and backups.
Capacity is the easy half of a backup. What decides whether it is worth having is how long the restore takes, whether anyone verified the archive, and whether an attacker holding your production credentials can also delete the backups.
A shared slot and a dedicated node can cost the same per terabyte and behave nothing alike. Contended random IO, fair-use ceilings and shared address reputation are what separate them — along with everything a slot simply cannot run.
A VOD box is two machines pretending to be one: a large cold catalog and a small hot working set. Price them separately. From 2.7 GB per 1080p hour through 96 TB raw becoming 52 TiB usable, to why range requests are the argument for an NVMe tier.
All three are still shipping because they solve different problems. The interface ceilings, the queue models, the DWPD and power-loss specifications that actually matter, and how to pick the mix for your working set.
Eight 12 TB drives give you 96 TB raw and four sensible ways to arrange them. What each level costs in capacity, what it buys in redundancy, and how long a rebuild really takes.