Shared, distributed lock manager to coordinate activity. Components authenticate themselves to one another. Little rationale offered for this layout. Logging and Recovery Write-ahead logging. Log only meta-data updates.
Failure is detected in two ways.
Client does not hear back from a server. Lock manager asks for a lock back and doesn't get a reply. A recovery daemon is given ownership of the crashed logs and runs recovery. Making recovery work. Blocks are written to Petal before write locks are moved from one server to another.