diff --git a/lib/iscsi/conn.c b/lib/iscsi/conn.c
index f9531d696..1693cbb85 100644
--- a/lib/iscsi/conn.c
+++ b/lib/iscsi/conn.c
@@ -1153,8 +1153,8 @@ spdk_iscsi_conn_flush_pdus_internal(struct spdk_iscsi_conn *conn)
 	struct iovec *iov = iovs;
 	int iovcnt = 0;
 	int bytes = 0;
-	int total_length = 0;
-	uint32_t writev_offset;
+	uint32_t total_length = 0;
+	uint32_t mapped_length = 0;
 	struct spdk_iscsi_pdu *pdu;
 	int pdu_length;
 
@@ -1173,17 +1173,12 @@ spdk_iscsi_conn_flush_pdus_internal(struct spdk_iscsi_conn *conn)
 	 *  But extra overhead is negligible.
 	 */
 	while (pdu != NULL && ((num_iovs - iovcnt) >= 5)) {
-		pdu_length = spdk_iscsi_get_pdu_length(pdu,
-						       conn->header_digest,
-						       conn->data_digest);
-		iovcnt += spdk_iscsi_build_iovs(conn, &iovs[iovcnt], pdu);
-		total_length += pdu_length;
+		iovcnt += spdk_iscsi_build_iovs(conn, &iovs[iovcnt], pdu,
+						&mapped_length);
+		total_length += mapped_length;
 		pdu = TAILQ_NEXT(pdu, tailq);
 	}
 
-	writev_offset = TAILQ_FIRST(&conn->write_pdu_list)->writev_offset;
-	total_length -= writev_offset;
-
 	spdk_trace_record(TRACE_ISCSI_FLUSH_WRITEBUF_START, conn->id, total_length, 0, iovcnt);
 
 	bytes = spdk_sock_writev(conn->sock, iov, iovcnt);
diff --git a/lib/iscsi/iscsi.c b/lib/iscsi/iscsi.c
index 2c1bab467..1525c1082 100644
--- a/lib/iscsi/iscsi.c
+++ b/lib/iscsi/iscsi.c
@@ -565,13 +565,14 @@ spdk_iscsi_read_pdu(struct spdk_iscsi_conn *conn, struct spdk_iscsi_pdu **_pdu)
 
 int
 spdk_iscsi_build_iovs(struct spdk_iscsi_conn *conn, struct iovec *iovs,
-		      struct spdk_iscsi_pdu *pdu)
+		      struct spdk_iscsi_pdu *pdu, uint32_t *_mapped_length)
 {
 	int iovcnt = 0;
 	int enable_digest;
 	uint32_t total_ahs_len;
 	uint32_t data_len;
 	uint32_t iov_offset;
+	uint32_t mapped_length = 0;
 
 	total_ahs_len = pdu->bhs.total_ahs_len;
 	data_len = DGET24(pdu->bhs.data_segment_len);
@@ -591,6 +592,7 @@ spdk_iscsi_build_iovs(struct spdk_iscsi_conn *conn, struct iovec *iovs,
 	} else {
 		iovs[iovcnt].iov_base = (uint8_t *)&pdu->bhs + iov_offset;
 		iovs[iovcnt].iov_len = ISCSI_BHS_LEN - iov_offset;
+		mapped_length += ISCSI_BHS_LEN - iov_offset;
 		iov_offset = 0;
 		iovcnt++;
 	}
@@ -601,6 +603,7 @@ spdk_iscsi_build_iovs(struct spdk_iscsi_conn *conn, struct iovec *iovs,
 		} else {
 			iovs[iovcnt].iov_base = pdu->ahs + iov_offset;
 			iovs[iovcnt].iov_len = 4 * total_ahs_len - iov_offset;
+			mapped_length += 4 * total_ahs_len - iov_offset;
 			iov_offset = 0;
 			iovcnt++;
 		}
@@ -613,6 +616,7 @@ spdk_iscsi_build_iovs(struct spdk_iscsi_conn *conn, struct iovec *iovs,
 		} else {
 			iovs[iovcnt].iov_base = pdu->header_digest + iov_offset;
 			iovs[iovcnt].iov_len = ISCSI_DIGEST_LEN - iov_offset;
+			mapped_length += ISCSI_DIGEST_LEN - iov_offset;
 			iov_offset = 0;
 			iovcnt++;
 		}
@@ -625,6 +629,7 @@ spdk_iscsi_build_iovs(struct spdk_iscsi_conn *conn, struct iovec *iovs,
 		} else {
 			iovs[iovcnt].iov_base = pdu->data + iov_offset;
 			iovs[iovcnt].iov_len = data_len - iov_offset;
+			mapped_length += data_len - iov_offset;
 			iov_offset = 0;
 			iovcnt++;
 		}
@@ -635,10 +640,15 @@ spdk_iscsi_build_iovs(struct spdk_iscsi_conn *conn, struct iovec *iovs,
 		if (iov_offset < ISCSI_DIGEST_LEN) {
 			iovs[iovcnt].iov_base = pdu->data_digest + iov_offset;
 			iovs[iovcnt].iov_len = ISCSI_DIGEST_LEN - iov_offset;
+			mapped_length += ISCSI_DIGEST_LEN - iov_offset;
 			iovcnt++;
 		}
 	}
 
+	if (_mapped_length != NULL) {
+		*_mapped_length = mapped_length;
+	}
+
 	return iovcnt;
 }
 
diff --git a/lib/iscsi/iscsi.h b/lib/iscsi/iscsi.h
index 459b46b57..91b436955 100644
--- a/lib/iscsi/iscsi.h
+++ b/lib/iscsi/iscsi.h
@@ -405,7 +405,8 @@ void spdk_iscsi_task_response(struct spdk_iscsi_conn *conn,
 			      struct spdk_iscsi_task *task);
 int spdk_iscsi_execute(struct spdk_iscsi_conn *conn, struct spdk_iscsi_pdu *pdu);
 int spdk_iscsi_build_iovs(struct spdk_iscsi_conn *conn,
-			  struct iovec *iovs, struct spdk_iscsi_pdu *pdu);
+			  struct iovec *iovs, struct spdk_iscsi_pdu *pdu,
+			  uint32_t *mapped_length);
 int spdk_iscsi_read_pdu(struct spdk_iscsi_conn *conn, struct spdk_iscsi_pdu **_pdu);
 void spdk_iscsi_task_mgmt_response(struct spdk_iscsi_conn *conn,
 				   struct spdk_iscsi_task *task);
diff --git a/test/unit/lib/iscsi/conn.c/conn_ut.c b/test/unit/lib/iscsi/conn.c/conn_ut.c
index 1e047f239..aa7362333 100644
--- a/test/unit/lib/iscsi/conn.c/conn_ut.c
+++ b/test/unit/lib/iscsi/conn.c/conn_ut.c
@@ -139,7 +139,7 @@ DEFINE_STUB_V(spdk_clear_all_transfer_task,
 
 DEFINE_STUB(spdk_iscsi_build_iovs, int,
 	    (struct spdk_iscsi_conn *conn, struct iovec *iov,
-	     struct spdk_iscsi_pdu *pdu),
+	     struct spdk_iscsi_pdu *pdu, uint32_t *mapped_length),
 	    0);
 
 DEFINE_STUB(spdk_iscsi_is_deferred_free_pdu, bool,
diff --git a/test/unit/lib/iscsi/iscsi.c/iscsi_ut.c b/test/unit/lib/iscsi/iscsi.c/iscsi_ut.c
index 5180f7545..631ca917d 100644
--- a/test/unit/lib/iscsi/iscsi.c/iscsi_ut.c
+++ b/test/unit/lib/iscsi/iscsi.c/iscsi_ut.c
@@ -1209,6 +1209,7 @@ build_iovs_test(void)
 	struct spdk_iscsi_pdu pdu = {};
 	struct iovec iovs[5] = {};
 	uint8_t *data;
+	uint32_t mapped_length = 0;
 	int rc;
 
 	conn.header_digest = true;
@@ -1223,7 +1224,7 @@ build_iovs_test(void)
 	pdu.bhs.opcode = ISCSI_OP_SCSI;
 
 	pdu.writev_offset = 0;
-	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu);
+	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu, &mapped_length);
 	CU_ASSERT(rc == 4);
 	CU_ASSERT(iovs[0].iov_base == (void *)&pdu.bhs);
 	CU_ASSERT(iovs[0].iov_len == ISCSI_BHS_LEN);
@@ -1233,9 +1234,10 @@ build_iovs_test(void)
 	CU_ASSERT(iovs[2].iov_len == 512);
 	CU_ASSERT(iovs[3].iov_base == (void *)pdu.data_digest);
 	CU_ASSERT(iovs[3].iov_len == ISCSI_DIGEST_LEN);
+	CU_ASSERT(mapped_length == ISCSI_BHS_LEN + ISCSI_DIGEST_LEN + 512 + ISCSI_DIGEST_LEN);
 
 	pdu.writev_offset = ISCSI_BHS_LEN / 2;
-	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu);
+	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu, &mapped_length);
 	CU_ASSERT(rc == 4);
 	CU_ASSERT(iovs[0].iov_base == (void *)((uint8_t *)&pdu.bhs + ISCSI_BHS_LEN / 2));
 	CU_ASSERT(iovs[0].iov_len == ISCSI_BHS_LEN / 2);
@@ -1245,9 +1247,10 @@ build_iovs_test(void)
 	CU_ASSERT(iovs[2].iov_len == 512);
 	CU_ASSERT(iovs[3].iov_base == (void *)pdu.data_digest);
 	CU_ASSERT(iovs[3].iov_len == ISCSI_DIGEST_LEN);
+	CU_ASSERT(mapped_length == ISCSI_BHS_LEN / 2 + ISCSI_DIGEST_LEN + 512 + ISCSI_DIGEST_LEN);
 
 	pdu.writev_offset = ISCSI_BHS_LEN;
-	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu);
+	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu, &mapped_length);
 	CU_ASSERT(rc == 3);
 	CU_ASSERT(iovs[0].iov_base == (void *)pdu.header_digest);
 	CU_ASSERT(iovs[0].iov_len == ISCSI_DIGEST_LEN);
@@ -1255,9 +1258,10 @@ build_iovs_test(void)
 	CU_ASSERT(iovs[1].iov_len == 512);
 	CU_ASSERT(iovs[2].iov_base == (void *)pdu.data_digest);
 	CU_ASSERT(iovs[2].iov_len == ISCSI_DIGEST_LEN);
+	CU_ASSERT(mapped_length == ISCSI_DIGEST_LEN + 512 + ISCSI_DIGEST_LEN);
 
 	pdu.writev_offset = ISCSI_BHS_LEN + ISCSI_DIGEST_LEN / 2;
-	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu);
+	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu, &mapped_length);
 	CU_ASSERT(rc == 3);
 	CU_ASSERT(iovs[0].iov_base == (void *)((uint8_t *)pdu.header_digest + ISCSI_DIGEST_LEN / 2));
 	CU_ASSERT(iovs[0].iov_len == ISCSI_DIGEST_LEN / 2);
@@ -1265,30 +1269,35 @@ build_iovs_test(void)
 	CU_ASSERT(iovs[1].iov_len == 512);
 	CU_ASSERT(iovs[2].iov_base == (void *)pdu.data_digest);
 	CU_ASSERT(iovs[2].iov_len == ISCSI_DIGEST_LEN);
+	CU_ASSERT(mapped_length == ISCSI_DIGEST_LEN / 2 + 512 + ISCSI_DIGEST_LEN);
 
 	pdu.writev_offset = ISCSI_BHS_LEN + ISCSI_DIGEST_LEN;
-	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu);
+	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu, &mapped_length);
 	CU_ASSERT(rc == 2);
 	CU_ASSERT(iovs[0].iov_base == (void *)pdu.data);
 	CU_ASSERT(iovs[0].iov_len == 512);
 	CU_ASSERT(iovs[1].iov_base == (void *)pdu.data_digest);
 	CU_ASSERT(iovs[1].iov_len == ISCSI_DIGEST_LEN);
+	CU_ASSERT(mapped_length == 512 + ISCSI_DIGEST_LEN);
 
 	pdu.writev_offset = ISCSI_BHS_LEN + ISCSI_DIGEST_LEN + 512;
-	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu);
+	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu, &mapped_length);
 	CU_ASSERT(rc == 1);
 	CU_ASSERT(iovs[0].iov_base == (void *)pdu.data_digest);
 	CU_ASSERT(iovs[0].iov_len == ISCSI_DIGEST_LEN);
+	CU_ASSERT(mapped_length == ISCSI_DIGEST_LEN);
 
 	pdu.writev_offset = ISCSI_BHS_LEN + ISCSI_DIGEST_LEN + 512 + ISCSI_DIGEST_LEN / 2;
-	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu);
+	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu, &mapped_length);
 	CU_ASSERT(rc == 1);
 	CU_ASSERT(iovs[0].iov_base == (void *)((uint8_t *)pdu.data_digest + ISCSI_DIGEST_LEN / 2));
 	CU_ASSERT(iovs[0].iov_len == ISCSI_DIGEST_LEN / 2);
+	CU_ASSERT(mapped_length == ISCSI_DIGEST_LEN / 2);
 
 	pdu.writev_offset = ISCSI_BHS_LEN + ISCSI_DIGEST_LEN + 512 + ISCSI_DIGEST_LEN;
-	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu);
+	rc = spdk_iscsi_build_iovs(&conn, iovs, &pdu, &mapped_length);
 	CU_ASSERT(rc == 0);
+	CU_ASSERT(mapped_length == 0);
 
 	free(data);
 }