[jarnold]

(I'm going to have some bias here as I've done Swift deployments as well.)

One of the advantages of using something like Swift for long-term storage is it's simplicity of how data is stored on disk. Data isn't chunked up and distributed throughout a cluster. Each replica is whole and on disk. And, as notmyname, mentions there are auditors that continuously run to check for bitrot and to ensure replicas are in place. The data is extremely durable in a swift cluster if you deploy and configure everything right.

I've done most of my price modeling for petabyte-scale deployments, but it actually has good scaling-down properties as well. If you're concerned about power, 2.5" drives may be an option. Although I would avoid 'green' drives as Swift tends to keep the drives quite active (replica and integrity checks) and you won't see much benefit.