diff --git a/src/SnapshotPayloadParseState.cpp b/src/SnapshotPayloadParseState.cpp
index 83bea31eb..123bd4e35 100644
--- a/src/SnapshotPayloadParseState.cpp
+++ b/src/SnapshotPayloadParseState.cpp
@@ -233,11 +233,6 @@ void SnapshotPayloadParseState::trimState() {
     
     if (stackParse.empty()) {
         flushQueuedKeys();
-        while (*insertsInFlight > 0) {
-            // TODO: ProcessEventsWhileBlocked
-            aeReleaseLock();
-            aeAcquireLock();
-        }
     }
 }
 
diff --git a/src/SnapshotPayloadParseState.h b/src/SnapshotPayloadParseState.h
index 29ac28fb6..91e9bc956 100644
--- a/src/SnapshotPayloadParseState.h
+++ b/src/SnapshotPayloadParseState.h
@@ -63,4 +63,5 @@ class SnapshotPayloadParseState {
     void pushValue(const char *rgch, long long cch);
     void pushValue(long long value);
     bool shouldThrottle() const { return *insertsInFlight > (cserver.cthreads*4); }
+    bool hasIOInFlight() const { return *insertsInFlight > 0; }
 };
\ No newline at end of file
diff --git a/src/config.cpp b/src/config.cpp
index 749fb5746..0ac230a9f 100644
--- a/src/config.cpp
+++ b/src/config.cpp
@@ -3201,7 +3201,7 @@ standardConfig configs[] = {
     createIntConfig("overload-protect-tenacity", NULL, MODIFIABLE_CONFIG, 0, 100, g_pserver->overload_protect_tenacity, 10, INTEGER_CONFIG, NULL, NULL),
     createIntConfig("force-eviction-percent", NULL, MODIFIABLE_CONFIG, 0, 100, g_pserver->force_eviction_percent, 0, INTEGER_CONFIG, NULL, NULL),
     createBoolConfig("enable-async-rehash", NULL, MODIFIABLE_CONFIG, g_pserver->enable_async_rehash, 1, NULL, NULL),
-    createBoolConfig("enable-keydb-fastsync", NULL, MODIFIABLE_CONFIG, g_pserver->fEnableFastSync, 0, NULL, NULL),
+    createBoolConfig("enable-keydb-fastsync", NULL, MODIFIABLE_CONFIG, g_pserver->fEnableFastSync, 1, NULL, NULL),
 
 #ifdef USE_OPENSSL
     createIntConfig("tls-port", NULL, MODIFIABLE_CONFIG, 0, 65535, g_pserver->tls_port, 0, INTEGER_CONFIG, NULL, updateTLSPort), /* TCP port. */
diff --git a/src/replication.cpp b/src/replication.cpp
index 91b995991..d0c3d1b91 100644
--- a/src/replication.cpp
+++ b/src/replication.cpp
@@ -1059,7 +1059,7 @@ class replicationBuffer {
             while (checkClientOutputBufferLimits(replica)
               && (replica->flags.load(std::memory_order_relaxed) & CLIENT_CLOSE_ASAP) == 0) {
                 ul.unlock();
-                usleep(0);
+                usleep(1000);   // give 1ms for the I/O before we poll again
                 ul.lock();
             }
         }
@@ -2521,7 +2521,7 @@ size_t parseCount(const char *rgch, size_t cch, long long *pvalue) {
     return cchNumeral + 3;
 }
 
-bool readSnapshotBulkPayload(connection *conn, redisMaster *mi, rdbSaveInfo &rsi) {
+bool readFastSyncBulkPayload(connection *conn, redisMaster *mi, rdbSaveInfo &rsi) {
     int fUpdate = g_pserver->fActiveReplica || g_pserver->enable_multimaster;
     serverAssert(GlobalLocksAcquired());
     serverAssert(mi->master == nullptr);
@@ -2546,6 +2546,10 @@ bool readSnapshotBulkPayload(connection *conn, redisMaster *mi, rdbSaveInfo &rsi
         }
     }
 
+    if (mi->repl_state == REPL_STATE_WAIT_STORAGE_IO) {
+        goto LWaitIO;
+    }
+
     serverAssert(mi->parseState != nullptr);
     for (int iter = 0; iter < 10; ++iter) {
         if (mi->parseState->shouldThrottle())
@@ -2663,7 +2667,14 @@ bool readSnapshotBulkPayload(connection *conn, redisMaster *mi, rdbSaveInfo &rsi
     if (!fFinished)
         return false;
 
+LWaitIO:
+    if (mi->parseState->hasIOInFlight()) {
+        mi->repl_state = REPL_STATE_WAIT_STORAGE_IO;
+        return false;
+    }
+
     serverLog(LL_NOTICE, "Fast sync complete");
+    serverAssert(!mi->parseState->hasIOInFlight());
     delete mi->parseState;
     mi->parseState = nullptr;
     return true;
@@ -3040,7 +3051,7 @@ void readSyncBulkPayload(connection *conn) {
     }
 
     if (mi->isKeydbFastsync) {
-        if (!readSnapshotBulkPayload(conn, mi, rsi))
+        if (!readFastSyncBulkPayload(conn, mi, rsi))
             return;
     } else {
         if (!readSyncBulkPayloadRdb(conn, mi, rsi, usemark))
@@ -4807,6 +4818,10 @@ void replicationCron(void) {
     {
         redisMaster *mi = (redisMaster*)listNodeValue(lnMaster);
 
+        if (mi->repl_state == REPL_STATE_WAIT_STORAGE_IO && !mi->parseState->hasIOInFlight()) {
+            readSyncBulkPayload(mi->repl_transfer_s);
+        }
+
         std::unique_lock<decltype(mi->master->lock)> ulock;
         if (mi->master != nullptr)
             ulock = decltype(ulock)(mi->master->lock);
diff --git a/src/server.h b/src/server.h
index 3826385a6..69966f9f3 100644
--- a/src/server.h
+++ b/src/server.h
@@ -612,6 +612,7 @@ typedef enum {
     REPL_STATE_RECEIVE_PSYNC_REPLY, /* Wait for PSYNC reply */
     /* --- End of handshake states --- */
     REPL_STATE_TRANSFER,        /* Receiving .rdb from master */
+    REPL_STATE_WAIT_STORAGE_IO,
     REPL_STATE_CONNECTED,       /* Connected to master */
 } repl_state;