We've had a few scares with failing SSDs in cloudvirts -- if we were to lose the wrong two drives in a row we'd suffer loss of user data.

The prudent thing is probably to keep spares on hands so we can replace things as they fail and avoid having two overlapping failures. Unfortunately there's quite a variety of drive sizes in the cloudvirts so this will be several different drives we'll have to keep around.

This task is part of https://wikitech.wikimedia.org/wiki/Incident_documentation/20190213-cloudvps