I'm running a private testnet miner on a VPS with only 8 GB of hard drive space. Is there some measure I can take to reduce the size of the .ethash directory?
As per https://github.com/ethereum/wiki/wiki/Ethash-DAG#location (quoted below), it should be fine to delete the older DAGs and retain the latest one. However, just to be on the safer side, I prefer leaving back the latest two DAGs.
There may be many such DAGs stored in this directory; it is up to the client and/or user to remove out of date ones.