1. Bookkeeper is not able to reclaim disk space when it's full
If all disks are full or almost full, both major and minor compactions would be suspended, and only GC will be running. In the current design, this is the right thing to do, because when disks are full, EntryLogger can not allocate any new entry logs any more, and apart from that, the intention is to prevent disk usage from keep growing.
However, the problem is if we have a mixed of short-lived ledgers and long-lived ledgers in all entry logs, when disks are full, GC wouldn't be able to delete any entry logs, and if compaction is disabled, bookie can't reclaim any disk space any more by itself.
2. Compaction might keep generating duplicated data which would cause disk full
Currently, there's no transactional operation for compaction. In the current CompactionScannerFactory, if it fails to flush entry log file, or fails to flush ledgerCache, the data which is already flushed wouldn't be deleted, and the entry log that is being compacted will be retried again for the next time, which would generate duplicated data.
Moreover, if the entry log being compacted has long-lived data and the compaction keeps failing for some reason(e.g. corrupted entry, corrupted index), it would cause the BK disk usage keep growing until the either the entry log can be garbage collected, or disk full.