@LarsR thanks!
To save others the time from reading 136 replies, here’s a clearer summary:
Key Technical Details:
- Issue tracked at: ixsystems Jira NAS-131728 (I am not allowed to post links…)
- Matthew Ahrens explained in
gh:openzfs/zfs/pull/12225#issuecomment-1057679062(I am not allowed to post links…) that:- Old blocks must maintain their original deflation ratio when freed to prevent over-accounting
- A solution using “time-dependent deflation ratios” is possible but wasn’t implemented due to time constraints
- This could be fixed in the future with “RAIDZ Expansion improved space accounting”
Can you use the “hidden” space?
- Yes! The space is fully usable despite being underreported
- The system will let you write more data than the reported available space
- Only the reporting is affected, not actual storage capacity
- The pool will still function normally and safely store data
- You can write data up to the true physical capacity of the expanded pool
Credits to @Stux for seemingly doing most of the research in the previous topic. Please let me know whether any of my conclusions are wrong.