Very higher Disk Usage than Data Usage in insert-only environment

[Behrad Zari]

I was able to insert 100M keys (20K op/sec) to Couchbase, until my 100G partition got full, however with Couchbase sizing documentation and my data sizes, I should have been able to achieve around twice inserts.

My Couchbase Console shows:

Disk Usage:92.3GB
Data Usage:44.3GB

I don't expect compaction would help since I did no updates in my load test. Could anyone explain why is this happening?

Is compaction necessary in insert-only mode?