Cloudant hosts databases with a lot of different cloud hosting providers including Amazon, Rackspace, SoftLayer and Microsoft Azure. This way customers can choose where their database is hosted.
The database behind Cloudant, CouchDB uses an append-only file for it's data. To restore already used up space, a compaction must happen. When this happens is up to the database maintainer.
Since CouchDB is considered an AP (Available, Partition-Tolerant database management system), it is not really consistent (not all clients can have the same view of the data consistently) and the only way to achieve some "eventual consistency" is through replication and verification of data.