diff --git a/block/Makefile.objs b/block/Makefile.objs
index f068666..84952b1 100644
--- a/block/Makefile.objs
+++ b/block/Makefile.objs
@@ -23,6 +23,7 @@ block-obj-$(CONFIG_LIBSSH2) += ssh.o
 block-obj-y += accounting.o
 block-obj-y += write-threshold.o
 block-obj-y += backup.o
+block-obj-y += replication.o
 
 common-obj-y += stream.o
 common-obj-y += commit.o
diff --git a/block/replication.c b/block/replication.c
new file mode 100644
index 0000000..2124e2d
--- /dev/null
+++ b/block/replication.c
@@ -0,0 +1,443 @@
+#include "qemu-common.h"
+#include "block/block_int.h"
+#include "block/blockjob.h"
+#include "block/nbd.h"
+
+typedef struct BDRVReplicationState {
+    ReplicationMode mode;
+    int replication_state;
+    BlockDriverState *active_disk;
+    BlockDriverState *hidden_disk;
+    BlockDriverState *secondary_disk; /* nbd target */
+    int error;
+} BDRVReplicationState;
+
+enum {
+    BLOCK_REPLICATION_NONE,     /* block replication is not started */
+    BLOCK_REPLICATION_RUNNING,  /* block replication is running */
+    BLOCK_REPLICATION_DONE,     /* block replication is done(failover) */
+};
+
+#define COMMIT_CLUSTER_BITS 16
+#define COMMIT_CLUSTER_SIZE (1 << COMMIT_CLUSTER_BITS)
+#define COMMIT_SECTORS_PER_CLUSTER (COMMIT_CLUSTER_SIZE / BDRV_SECTOR_SIZE)
+
+static void replication_stop(BlockDriverState *bs, bool failover, Error **errp);
+
+#define REPLICATION_MODE        "mode"
+static QemuOptsList replication_runtime_opts = {
+    .name = "replication",
+    .head = QTAILQ_HEAD_INITIALIZER(replication_runtime_opts.head),
+    .desc = {
+        {
+            .name = REPLICATION_MODE,
+            .type = QEMU_OPT_STRING,
+        },
+        { /* end of list */ }
+    },
+};
+
+static int replication_open(BlockDriverState *bs, QDict *options,
+                            int flags, Error **errp)
+{
+    int ret;
+    BDRVReplicationState *s = bs->opaque;;
+    Error *local_err = NULL;
+    QemuOpts *opts = NULL;
+    const char *mode;
+
+    ret = -EINVAL;
+    opts = qemu_opts_create(&replication_runtime_opts, NULL, 0, &error_abort);
+    qemu_opts_absorb_qdict(opts, options, &local_err);
+    if (local_err) {
+        goto fail;
+    }
+
+    mode = qemu_opt_get(opts, REPLICATION_MODE);
+    if (!mode) {
+        error_setg(&local_err, "Missing the option mode");
+        goto fail;
+    }
+
+    if (!strcmp(mode, "primary")) {
+        s->mode = REPLICATION_MODE_PRIMARY;
+    } else if (!strcmp(mode, "secondary")) {
+        s->mode = REPLICATION_MODE_SECONDARY;
+    } else {
+        error_setg(&local_err,
+                   "The option mode's value should be primary or secondary");
+        goto fail;
+    }
+
+    return 0;
+
+fail:
+    qemu_opts_del(opts);
+    /* propagate error */
+    if (local_err) {
+        error_propagate(errp, local_err);
+    }
+    return ret;
+}
+
+static void replication_close(BlockDriverState *bs)
+{
+    BDRVReplicationState *s = bs->opaque;
+
+    if (s->replication_state == BLOCK_REPLICATION_RUNNING) {
+        replication_stop(bs, false, NULL);
+    }
+}
+
+static int64_t replication_getlength(BlockDriverState *bs)
+{
+    return bdrv_getlength(bs->file);
+}
+
+static int replication_get_io_status(BDRVReplicationState *s)
+{
+    switch (s->replication_state) {
+    case BLOCK_REPLICATION_NONE:
+        return -EIO;
+    case BLOCK_REPLICATION_RUNNING:
+        return 0;
+    case BLOCK_REPLICATION_DONE:
+        return s->mode == REPLICATION_MODE_PRIMARY ? -EIO : 1;
+    default:
+        abort();
+    }
+}
+
+static int replication_return_value(BDRVReplicationState *s, int ret)
+{
+    if (s->mode == REPLICATION_MODE_SECONDARY) {
+        return ret;
+    }
+
+    if (ret < 0) {
+        s->error = ret;
+        ret = 0;
+    }
+
+    return ret;
+}
+
+static coroutine_fn int replication_co_readv(BlockDriverState *bs,
+                                             int64_t sector_num,
+                                             int remaining_sectors,
+                                             QEMUIOVector *qiov)
+{
+    BDRVReplicationState *s = bs->opaque;
+    int ret;
+
+    if (s->mode == REPLICATION_MODE_PRIMARY) {
+        /* We only use it to forward primary write requests */
+        return -EIO;
+    }
+
+    ret = replication_get_io_status(s);
+    if (ret < 0) {
+        return ret;
+    }
+
+    /*
+     * After failover, because we don't commit active disk/hidden disk
+     * to secondary disk(nbd target), so we should read from active disk
+     * directly.
+     */
+    ret = bdrv_co_readv(bs->file, sector_num, remaining_sectors, qiov);
+    return replication_return_value(s, ret);
+}
+
+static coroutine_fn int replication_co_writev(BlockDriverState *bs,
+                                              int64_t sector_num,
+                                              int remaining_sectors,
+                                              QEMUIOVector *qiov)
+{
+    BDRVReplicationState *s = bs->opaque;
+    QEMUIOVector hd_qiov;
+    uint64_t bytes_done = 0;
+    BlockDriverState *top = bs->file;
+    BlockDriverState *base = s->secondary_disk;
+    BlockDriverState *target;
+    int ret, n;
+
+    ret = replication_get_io_status(s);
+    if (ret < 0) {
+        return ret;
+    }
+
+    if (ret == 0) {
+        ret = bdrv_co_writev(bs->file, sector_num, remaining_sectors, qiov);
+        return replication_return_value(s, ret);
+    }
+
+    /*
+     * Only write to active disk if the sectors have
+     * already been allocated in active disk/hidden disk.
+     */
+    qemu_iovec_init(&hd_qiov, qiov->niov);
+    while (remaining_sectors > 0) {
+        ret = bdrv_is_allocated_above(top, base, sector_num,
+                                      remaining_sectors, &n);
+        if (ret < 0) {
+            return ret;
+        }
+
+        qemu_iovec_reset(&hd_qiov);
+        qemu_iovec_concat(&hd_qiov, qiov, bytes_done, n * 512);
+
+        target = ret ? top: base;
+        ret = bdrv_co_writev(target, sector_num, n, &hd_qiov);
+        if (ret < 0) {
+            return ret;
+        }
+
+        remaining_sectors -= n;
+        sector_num += n;
+        bytes_done += n * BDRV_SECTOR_SIZE;
+    }
+
+    return 0;
+}
+
+static coroutine_fn int replication_co_discard(BlockDriverState *bs,
+                                               int64_t sector_num,
+                                               int nb_sectors)
+{
+    BDRVReplicationState *s = bs->opaque;
+    int ret;
+
+    ret = replication_get_io_status(s);
+    if (ret < 0) {
+        return ret;
+    }
+
+    if (ret == 1) {
+        /* It is secondary qemu and we are after failover */
+        ret = bdrv_co_discard(s->secondary_disk, sector_num, nb_sectors);
+        if (ret) {
+            return ret;
+        }
+    }
+
+    ret = bdrv_co_discard(bs->file, sector_num, nb_sectors);
+    return replication_return_value(s, ret);
+}
+
+static bool replication_recurse_is_first_non_filter(BlockDriverState *bs,
+                                                    BlockDriverState *candidate)
+{
+    return bdrv_recurse_is_first_non_filter(bs->file, candidate);
+}
+
+static void secondary_do_checkpoint(BDRVReplicationState *s, Error **errp)
+{
+    Error *local_err = NULL;
+    int ret;
+
+    if (!s->secondary_disk->job) {
+        error_setg(errp, "Backup job is cancelled unexpectedly");
+        return;
+    }
+
+    block_job_do_checkpoint(s->secondary_disk->job, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    ret = s->active_disk->drv->bdrv_make_empty(s->active_disk);
+    if (ret < 0) {
+        error_setg(errp, "Cannot make active disk empty");
+        return;
+    }
+
+    ret = s->hidden_disk->drv->bdrv_make_empty(s->hidden_disk);
+    if (ret < 0) {
+        error_setg(errp, "Cannot make hidden disk empty");
+        return;
+    }
+}
+
+static void backup_job_completed(void *opaque, int ret)
+{
+    BDRVReplicationState *s = opaque;
+
+    if (s->replication_state != BLOCK_REPLICATION_DONE) {
+        /* The backup job is cancelled unexpectedly */
+        s->error = -EIO;
+    }
+
+    bdrv_put_ref_bh_schedule(s->secondary_disk);
+}
+
+static void replication_start(BlockDriverState *bs, ReplicationMode mode,
+                              Error **errp)
+{
+    BDRVReplicationState *s = bs->opaque;
+    int64_t active_length, hidden_length, nbd_length;
+    AioContext *aio_context;
+    Error *local_err = NULL;
+
+    if (s->replication_state != BLOCK_REPLICATION_NONE) {
+        error_setg(errp, "Block replication is running or done");
+        return;
+    }
+
+    if (s->mode != mode) {
+        error_setg(errp, "Invalid parameter 'mode'");
+        return;
+    }
+
+    switch (s->mode) {
+    case REPLICATION_MODE_PRIMARY:
+        break;
+    case REPLICATION_MODE_SECONDARY:
+        s->active_disk = bs->file;
+        if (!bs->file->backing_hd) {
+            error_setg(errp, "Active disk doesn't have backing file");
+            return;
+        }
+
+        s->hidden_disk = s->active_disk->backing_hd;
+        if (!s->hidden_disk->backing_hd) {
+            error_setg(errp, "Hidden disk doesn't have backing file");
+            return;
+        }
+
+        s->secondary_disk = s->hidden_disk->backing_hd;
+        if (!s->secondary_disk->blk) {
+            error_setg(errp, "The secondary disk doesn't have block backend");
+            return;
+        }
+
+        /* verify the length */
+        active_length = bdrv_getlength(s->active_disk);
+        hidden_length = bdrv_getlength(s->hidden_disk);
+        nbd_length = bdrv_getlength(s->secondary_disk);
+        if (active_length < 0 || hidden_length < 0 || nbd_length < 0 ||
+            active_length != hidden_length || hidden_length != nbd_length) {
+            error_setg(errp, "active disk, hidden disk, nbd target's length"
+                       " are not the same");
+            return;
+        }
+
+        if (!s->active_disk->drv->bdrv_make_empty ||
+            !s->hidden_disk->drv->bdrv_make_empty) {
+            error_setg(errp,
+                       "active disk or hidden disk doesn't support make_empty");
+            return;
+        }
+
+        /* start backup job now */
+        bdrv_op_unblock(s->hidden_disk, BLOCK_OP_TYPE_BACKUP_TARGET,
+                        s->active_disk->backing_blocker);
+        bdrv_op_unblock(s->secondary_disk, BLOCK_OP_TYPE_BACKUP_SOURCE,
+                        s->hidden_disk->backing_blocker);
+        bdrv_ref(s->hidden_disk);
+
+        aio_context = bdrv_get_aio_context(bs);
+        aio_context_acquire(aio_context);
+        bdrv_set_aio_context(s->secondary_disk, aio_context);
+        backup_start(s->secondary_disk, s->hidden_disk, 0,
+                     MIRROR_SYNC_MODE_NONE, NULL, BLOCKDEV_ON_ERROR_REPORT,
+                     BLOCKDEV_ON_ERROR_REPORT, backup_job_completed,
+                     s, &local_err);
+        aio_context_release(aio_context);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            bdrv_unref(s->hidden_disk);
+            return;
+        }
+        break;
+    default:
+        abort();
+    }
+
+    s->replication_state = BLOCK_REPLICATION_RUNNING;
+
+    if (s->mode == REPLICATION_MODE_SECONDARY) {
+        secondary_do_checkpoint(s, errp);
+    }
+
+    s->error = 0;
+}
+
+static void replication_do_checkpoint(BlockDriverState *bs, Error **errp)
+{
+    BDRVReplicationState *s = bs->opaque;
+
+    if (s->replication_state != BLOCK_REPLICATION_RUNNING) {
+        error_setg(errp, "Block replication is not running");
+        return;
+    }
+
+    if (s->error) {
+        error_setg(errp, "I/O error occurs");
+        return;
+    }
+
+    if (s->mode == REPLICATION_MODE_SECONDARY) {
+        secondary_do_checkpoint(s, errp);
+    }
+}
+
+static void replication_stop(BlockDriverState *bs, bool failover, Error **errp)
+{
+    BDRVReplicationState *s = bs->opaque;
+
+    if (s->replication_state != BLOCK_REPLICATION_RUNNING) {
+        error_setg(errp, "Block replication is not running");
+        return;
+    }
+
+    s->replication_state = BLOCK_REPLICATION_DONE;
+
+    switch (s->mode) {
+    case REPLICATION_MODE_PRIMARY:
+        break;
+    case REPLICATION_MODE_SECONDARY:
+        if (!failover) {
+            secondary_do_checkpoint(s, errp);
+            return;
+        }
+
+        if (s->secondary_disk->job) {
+            block_job_cancel(s->secondary_disk->job);
+        }
+        break;
+    default:
+        abort();
+    }
+}
+
+BlockDriver bdrv_replication = {
+    .format_name                = "replication",
+    .protocol_name              = "replication",
+    .instance_size              = sizeof(BDRVReplicationState),
+
+    .bdrv_open                  = replication_open,
+    .bdrv_close                 = replication_close,
+
+    .bdrv_getlength             = replication_getlength,
+    .bdrv_co_readv              = replication_co_readv,
+    .bdrv_co_writev             = replication_co_writev,
+    .bdrv_co_discard            = replication_co_discard,
+
+    .is_filter                  = true,
+    .bdrv_recurse_is_first_non_filter = replication_recurse_is_first_non_filter,
+
+    .bdrv_start_replication     = replication_start,
+    .bdrv_do_checkpoint         = replication_do_checkpoint,
+    .bdrv_stop_replication      = replication_stop,
+
+    .has_variable_length        = true,
+};
+
+static void bdrv_replication_init(void)
+{
+    bdrv_register(&bdrv_replication);
+}
+
+block_init(bdrv_replication_init);
