Currently, trashed blocks are not included in any of the stats logged by keep-balance, so the only way to estimate storage consumed by trash is to subtract the reported "total usage" from the usage reported by the backend filesystem/cloud provider, and assume all of it is attributable to trashed blocks.

keepstore should provide an API for listing/summarizing trashed blocks on each volume, and keep-balance should use that to compute & report the total #blocks and #bytes.