diff --git a/kernel/mars.h b/kernel/mars.h
index 8dba794c..f79950cb 100644
--- a/kernel/mars.h
+++ b/kernel/mars.h
@@ -156,6 +156,9 @@ enum _MREF_FLAGS {
 	_MREF_WRITE,
 	_MREF_MAY_WRITE,
 	_MREF_SKIP_SYNC,
+	_MREF_NODATA, /* only useful for chksum reading */
+	/* Checksum bits, starting at the upper half */
+	_MREF_CHKSUM_MD5_OLD = 16,
 };
 
 #define MREF_UPTODATE        (1UL << _MREF_UPTODATE)
@@ -164,6 +167,9 @@ enum _MREF_FLAGS {
 #define MREF_WRITE           (1UL << _MREF_WRITE)
 #define MREF_MAY_WRITE       (1UL << _MREF_MAY_WRITE)
 #define MREF_SKIP_SYNC       (1UL << _MREF_SKIP_SYNC)
+#define MREF_NODATA          (1UL << _MREF_NODATA)
+#define MREF_CHKSUM_MD5_OLD  (1UL << _MREF_CHKSUM_MD5_OLD)
+#define MREF_CHKSUM_ANY      (MREF_CHKSUM_MD5_OLD)
 
 #define MREF_OBJECT(OBJTYPE)						\
 	CALLBACK_OBJECT(OBJTYPE);					\
@@ -173,7 +179,6 @@ enum _MREF_FLAGS {
 	int    ref_len;							\
 	int    ref_prio;						\
 	int    ref_timeout;						\
-	int    ref_cs_mode; /* 0 = off, 1 = checksum + data, 2 = checksum only */	\
 	/* shared */							\
 	__u32  ref_flags;						\
 	/* maintained by the ref implementation, readable for callers */ \
@@ -187,6 +192,7 @@ enum _MREF_FLAGS {
 	int    ref_rw;							\
 	int    ref_may_write;						\
 	bool   ref_skip_sync; /* skip sync for this particular mref */	\
+	int    ref_cs_mode; /* 0 = off, 1 = checksum + data, 2 = checksum only */ \
 	/* internal */							\
 	atomic_trace_t ref_at;						\
 	bool   ref_initialized; /* internally used for checking */	\
diff --git a/kernel/mars_copy.c b/kernel/mars_copy.c
index 5266da5d..0be2b033 100644
--- a/kernel/mars_copy.c
+++ b/kernel/mars_copy.c
@@ -280,7 +280,9 @@ err:
 }
 
 static
-int _make_mref(struct copy_brick *brick, int index, int queue, void *data, loff_t pos, loff_t end_pos, __u32 flags, int cs_mode)
+int _make_mref(struct copy_brick *brick, int index, int queue, void *data,
+	       loff_t pos, loff_t end_pos,
+	       __u32 flags)
 {
 	struct mref_object *mref;
 	struct copy_mref_aspect *mref_a;
@@ -309,7 +311,6 @@ int _make_mref(struct copy_brick *brick, int index, int queue, void *data, loff_
 	mref->ref_flags = flags;
 	mref->ref_data = data;
 	mref->ref_pos = pos;
-	mref->ref_cs_mode = cs_mode;
 	offset = GET_OFFSET(pos);
 	len = COPY_CHUNK - offset;
 	if (pos + len > end_pos) {
@@ -374,6 +375,14 @@ void _update_percent(struct copy_brick *brick, bool force)
 	}
 }
 
+static inline
+__u32 _make_flags(bool verify_mode)
+{
+	if (!verify_mode)
+		return 0;
+	return MREF_NODATA | MREF_CHKSUM_ANY;
+}
+
 
 /* The heart of this brick.
  * State transition function of the finite automaton.
@@ -441,7 +450,9 @@ restart:
 		    is_read_limited(brick))
 			goto idle;
 
-		status = _make_mref(brick, index, 0, NULL, pos, brick->copy_end, 0, brick->verify_mode ? 2 : 0);
+		status = _make_mref(brick, index, 0, NULL,
+				    pos, brick->copy_end,
+				    _make_flags(brick->verify_mode));
 		if (unlikely(status < 0)) {
 			MARS_DBG("status = %d\n", status);
 			progress = status;
@@ -456,7 +467,9 @@ restart:
 		next_state = COPY_STATE_START2;
 		/* fallthrough */
 	case COPY_STATE_START2:
-		status = _make_mref(brick, index, 1, NULL, pos, brick->copy_end, 0, 2);
+		status = _make_mref(brick, index, 1, NULL,
+				    pos, brick->copy_end,
+				    _make_flags(true));
 		if (unlikely(status < 0)) {
 			MARS_DBG("status = %d\n", status);
 			progress = status;
@@ -491,7 +504,7 @@ restart:
 
 			if (len != mref1->ref_len) {
 				ok = false;
-			} else if (mref0->ref_cs_mode) {
+			} else if (mref0->ref_flags & MREF_CHKSUM_ANY) {
 				static unsigned char null[sizeof(mref0->ref_checksum)];
 				ok = !memcmp(mref0->ref_checksum, mref1->ref_checksum, sizeof(mref0->ref_checksum));
 				if (ok)
@@ -516,9 +529,12 @@ restart:
 			}
 		}
 
-		if (mref0->ref_cs_mode > 1) { // re-read, this time with data
+		if ((mref0->ref_flags & MREF_CHKSUM_ANY) && (mref0->ref_flags & MREF_NODATA)) {
+			/* re-read, this time with data */
 			_clear_mref(brick, index, 0);
-			status = _make_mref(brick, index, 0, NULL, pos, brick->copy_end, 0, 0);
+			status = _make_mref(brick, index, 0, NULL,
+					    pos, brick->copy_end,
+					    _make_flags(false));
 			if (unlikely(status < 0)) {
 				MARS_DBG("status = %d\n", status);
 				progress = status;
@@ -564,7 +580,9 @@ restart:
 			break;
 		}
 		/* start writeout */
-		status = _make_mref(brick, index, 1, mref0->ref_data, pos, pos + mref0->ref_len, MREF_WRITE | MREF_MAY_WRITE, 0);
+		status = _make_mref(brick, index, 1, mref0->ref_data,
+				    pos, pos + mref0->ref_len,
+				    MREF_WRITE | MREF_MAY_WRITE);
 		if (unlikely(status < 0)) {
 			MARS_DBG("status = %d\n", status);
 			progress = status;
diff --git a/kernel/mars_generic.c b/kernel/mars_generic.c
index 843e8f43..6b394b5f 100644
--- a/kernel/mars_generic.c
+++ b/kernel/mars_generic.c
@@ -204,7 +204,7 @@ void mref_checksum(struct mref_object *mref)
 	unsigned char checksum[mars_digest_size];
 	int len;
 
-	if (mref->ref_cs_mode <= 0 || !mref->ref_data)
+	if (!(mref->ref_flags & MREF_CHKSUM_ANY) || !mref->ref_data)
 		return;
 
 	mars_digest(checksum, mref->ref_data, mref->ref_len);
diff --git a/kernel/mars_net.c b/kernel/mars_net.c
index c6cbba04..158829dc 100644
--- a/kernel/mars_net.c
+++ b/kernel/mars_net.c
@@ -1221,6 +1221,12 @@ static void _send_deprecated(struct mref_object *mref)
 
 	if (mref->ref_flags & MREF_SKIP_SYNC)
 		mref->ref_skip_sync = true;
+
+	if (mref->ref_flags & MREF_CHKSUM_ANY) {
+		mref->ref_cs_mode = 1;
+		if (mref->ref_flags & MREF_NODATA)
+			mref->ref_cs_mode = 2;
+	}
 }
 
 int mars_send_mref(struct mars_socket *msock, struct mref_object *mref, bool cork)
@@ -1235,7 +1241,9 @@ int mars_send_mref(struct mars_socket *msock, struct mref_object *mref, bool cor
 	/* compatibility to old protocol */
 	_send_deprecated(mref);
 
-	if ((mref->ref_flags & MREF_WRITE) && mref->ref_data && mref->ref_cs_mode < 2)
+	if ((mref->ref_flags & MREF_WRITE) &&
+	    mref->ref_data &&
+	    !(mref->ref_flags & MREF_NODATA))
 		cmd.cmd_code |= CMD_FLAG_HAS_DATA;
 
 	if (!cork || !msock->s_pos)
@@ -1262,6 +1270,8 @@ EXPORT_SYMBOL_GPL(mars_send_mref);
  */
 static void _recv_deprecated(struct mref_object *mref)
 {
+	int cs_mode;
+
 	/* compatibility to old protocol */
 	if (mref->ref_rw) {
 		mref->ref_rw = 0;
@@ -1276,6 +1286,14 @@ static void _recv_deprecated(struct mref_object *mref)
 		mref->ref_skip_sync = false;
 		mref->ref_flags |= MREF_SKIP_SYNC;
 	}
+
+	cs_mode = mref->ref_cs_mode;
+	if (cs_mode) {
+		mref->ref_cs_mode = 0;
+		mref->ref_flags |= MREF_CHKSUM_MD5_OLD;
+		if (cs_mode > 1)
+			mref->ref_flags |= MREF_NODATA;
+	}
 }
 
 int mars_recv_mref(struct mars_socket *msock, struct mref_object *mref, struct mars_cmd *cmd)
@@ -1322,7 +1340,7 @@ int mars_send_cb(struct mars_socket *msock, struct mref_object *mref, bool cork)
 
 	if (!(mref->ref_flags & MREF_WRITE) &&
 	    mref->ref_data &&
-	    mref->ref_cs_mode < 2)
+	    !(mref->ref_flags & MREF_NODATA))
 		cmd.cmd_code |= CMD_FLAG_HAS_DATA;
 
 	if (!cork || !msock->s_pos)
diff --git a/kernel/mars_server.c b/kernel/mars_server.c
index 20d9a4d2..019239f9 100644
--- a/kernel/mars_server.c
+++ b/kernel/mars_server.c
@@ -257,7 +257,7 @@ int server_io(struct server_brick *brick, struct mars_socket *sock, struct mars_
 	SETUP_CALLBACK(mref, server_endio, mref_a);
 
 	amount = 0;
-	if (mref->ref_cs_mode < 2)
+	if (!(mref->ref_flags & MREF_NODATA))
 		amount = (mref->ref_len - 1) / 1024 + 1;
 	mars_limit_sleep(&server_limiter, amount);