>> In any case: Monitoring disk-space is very very important. > > So, why doesn't cassandra monitor it itself and stop accepting writes if it > runs out of space?
For one thing, it's non-trivial to do accurately because disk space usage varies over time due to background compaction and/or anti-compaction. Compaction will require different amount of diskspaces depending on the nature of writes (e.g., if all writes are removals compaction takes much less space than if all writes are non-overwriting inserts). Maybe the maximum possible disk space use can be kept track of in a conservative fashion (assuming all writes are non-overwriting inserts, assuming a maximally disk-space intensive repair will be run, etc) and then behave appropriately based on that. If someone has a use case where the cluster is sufficiently close to running out of disk space (but it works for the particular use-case), such a feature could be turned off. But it would make it less easy to accidentally write yourself into a corner. -- / Peter Schuller
