Ceph Operation v/s Subop Latency

In Ceph, operation latency and subop latency measure different aspects of I/O processing:

Operation Latency

• Measures the total time taken for a client operation (read/write) to complete
• Includes the entire path from client request to completion
• Represented by metrics like op_latency, op_r_latency, and op_w_latency

Subop Latency

• Measures the time taken for internal replication operations between OSDs
• Occurs when primary OSD replicates data to secondary OSDs
• Represented by the subop_latency metric
• Part of Ceph’s replication process for data durability

Relationship

1. A client operation (op) may trigger multiple suboperations (subops)
2. Subops are internal operations between OSDs for replication
3. Total operation latency includes subop latency when replication is involved

References

Ceph OSD Metrics Documentation

Ceph Performance Counters