diff --git a/src/replica/replica_stub.cpp b/src/replica/replica_stub.cpp
index a51ea4d7b6..639f0ab4a8 100644
--- a/src/replica/replica_stub.cpp
+++ b/src/replica/replica_stub.cpp
@@ -100,22 +100,15 @@
 
 namespace {
 
-const char *kMaxConcurrentBulkLoadDownloadingCountDesc =
-    "The maximum concurrent bulk load downloading replica count.";
-
 const char *kMaxReplicasOnLoadForEachDiskDesc =
     "The max number of replicas that are allowed to be loaded simultaneously for each disk dir.";
 
 const char *kLoadReplicaMaxWaitTimeMsDesc = "The max waiting time for replica loading to complete.";
 
-} // anonymous namespace
+const char *kMaxConcurrentBulkLoadDownloadingCountDesc =
+    "The maximum concurrent bulk load downloading replica count.";
 
-DSN_DEFINE_int32(replication,
-                 max_concurrent_bulk_load_downloading_count,
-                 5,
-                 kMaxConcurrentBulkLoadDownloadingCountDesc);
-DSN_DEFINE_validator(max_concurrent_bulk_load_downloading_count,
-                     [](int32_t value) -> bool { return value >= 0; });
+} // anonymous namespace
 
 METRIC_DEFINE_gauge_int64(server,
                           total_replicas,
@@ -290,6 +283,13 @@ DSN_TAG_VARIABLE(load_replica_max_wait_time_ms, FT_MUTABLE);
 DSN_DEFINE_validator(load_replica_max_wait_time_ms,
                      [](uint64_t value) -> bool { return value > 0; });
 
+DSN_DEFINE_int32(replication,
+                 max_concurrent_bulk_load_downloading_count,
+                 5,
+                 kMaxConcurrentBulkLoadDownloadingCountDesc);
+DSN_DEFINE_validator(max_concurrent_bulk_load_downloading_count,
+                     [](int32_t value) -> bool { return value >= 0; });
+
 DSN_DEFINE_bool(replication,
                 deny_client_on_start,
                 false,
@@ -540,7 +540,11 @@ void replica_stub::load_replica(dir_node *disk_node,
                                 replica_map_by_gpid &reps,
                                 std::atomic<size_t> &finished_dir_count)
 {
-    SCOPED_LOG_TIMING(INFO, "on loading {}:{}", disk_node->tag, replica_dir);
+    // Measure execution time for loading a replica dir.
+    //
+    // TODO(wangdan): support decimal milliseconds or microseconds, since loading a small
+    // replica tends to spend less than 1 milliseconds and show "0ms" in logging.
+    SCOPED_LOG_TIMING(INFO, "on loading replica dir {}:{}", disk_node->tag, replica_dir);
 
     LOG_INFO("loading replica: replica_dir={}:{}", disk_node->tag, replica_dir);
 
@@ -588,14 +592,19 @@ void replica_stub::load_replica(dir_node *disk_node,
 
 void replica_stub::load_replicas(replica_map_by_gpid &reps)
 {
+    // Measure execution time for loading all replicas from all healthy disks without IO errors.
+    //
+    // TODO(wangdan): show both the size of output replicas and execution time on just one
+    // logging line.
     SCOPED_LOG_TIMING(INFO, "on loading replicas");
 
     const auto &disks = get_all_disk_dirs();
 
-    // The max index of dirs that are currently being loaded for each disk. The dirs with
-    // higher indexes have not begun to be loaded (namely pushed into the queue).
+    // The max index of dirs that are currently being loaded for each disk, which means the dirs
+    // with higher indexes have not begun to be loaded (namely pushed into the queue).
     std::vector<size_t> replica_dir_indexes(disks.size(), 0);
 
+    // Each loader is for a replica dir, including its path and loading task.
     struct replica_dir_loader
     {
         size_t replica_dir_index;
@@ -608,6 +617,9 @@ void replica_stub::load_replicas(replica_map_by_gpid &reps)
     // the queue.
     std::vector<std::queue<replica_dir_loader>> load_disk_queues(disks.size());
 
+    // The number of loading replica dirs that have been finished for each disk, used to show
+    // current progress.
+    //
     // TODO(wangdan): calculate the number of successful or failed loading of replica dirs,
     // and the number for each reason if failed.
     std::vector<std::atomic<size_t>> finished_replica_dirs(disks.size());
@@ -639,7 +651,7 @@ void replica_stub::load_replicas(replica_map_by_gpid &reps)
             auto &replica_dir_index = replica_dir_indexes[disk_index];
             if (replica_dir_index >= replica_dirs.size()) {
                 // All of the replicas for the disk `disks[disk_index]` have begun to be loaded,
-                // thus just skip.
+                // thus just skip to next disk.
                 ++finished_disks;
                 continue;
             }
diff --git a/src/replica/replica_stub.h b/src/replica/replica_stub.h
index 284f178836..d6162bf8c3 100644
--- a/src/replica/replica_stub.h
+++ b/src/replica/replica_stub.h
@@ -384,7 +384,7 @@ class replica_stub : public serverlet<replica_stub>, public ref_counter
         std::vector<std::string> replica_dirs;
     };
 
-    // Get the absolute dirs of all replicas for all disks.
+    // Get the absolute dirs of all replicas for all healthy disks without IO errors.
     std::vector<disk_replicas_info> get_all_disk_dirs() const;
 
     // Get the replica dir name from a potentially longer path (`dir` could be an absolute