diff --git a/block/mirror.c b/block/mirror.c
index 58a6f89..d0544e3 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -24,9 +24,8 @@

 #define SLICE_TIME    100000000ULL /* ns */
 #define MAX_IN_FLIGHT 16
-#define MAX_IO_SECTORS ((1 << 20) >> BDRV_SECTOR_BITS) /* 1 Mb */
-#define DEFAULT_MIRROR_BUF_SIZE \
-    (MAX_IN_FLIGHT * MAX_IO_SECTORS * BDRV_SECTOR_SIZE)
+#define MAX_IO_BYTES (1 << 20) /* 1 Mb */
+#define DEFAULT_MIRROR_BUF_SIZE (MAX_IN_FLIGHT * MAX_IO_BYTES)

 /* The mirroring buffer is a list of granularity-sized chunks.
  * Free chunks are organized in a list.
@@ -67,11 +66,11 @@ typedef struct MirrorBlockJob {
     uint64_t last_pause_ns;
     unsigned long *in_flight_bitmap;
     int in_flight;
-    int64_t sectors_in_flight;
+    int64_t bytes_in_flight;
     int ret;
     bool unmap;
     bool waiting_for_io;
-    int target_cluster_sectors;
+    int target_cluster_size;
     int max_iov;
     bool initial_zeroing_ongoing;
 } MirrorBlockJob;
@@ -79,8 +78,8 @@ typedef struct MirrorBlockJob {
 typedef struct MirrorOp {
     MirrorBlockJob *s;
     QEMUIOVector qiov;
-    int64_t sector_num;
-    int nb_sectors;
+    int64_t offset;
+    uint64_t bytes;
 } MirrorOp;

 static BlockErrorAction mirror_error_action(MirrorBlockJob *s, bool read,
@@ -101,13 +100,12 @@ static void mirror_iteration_done(MirrorOp *op, int ret)
     MirrorBlockJob *s = op->s;
     struct iovec *iov;
     int64_t chunk_num;
-    int i, nb_chunks, sectors_per_chunk;
+    int i, nb_chunks;

-    trace_mirror_iteration_done(s, op->sector_num * BDRV_SECTOR_SIZE,
-                                op->nb_sectors * BDRV_SECTOR_SIZE, ret);
+    trace_mirror_iteration_done(s, op->offset, op->bytes, ret);

     s->in_flight--;
-    s->sectors_in_flight -= op->nb_sectors;
+    s->bytes_in_flight -= op->bytes;
     iov = op->qiov.iov;
     for (i = 0; i < op->qiov.niov; i++) {
         MirrorBuffer *buf = (MirrorBuffer *) iov[i].iov_base;
@@ -115,16 +113,15 @@ static void mirror_iteration_done(MirrorOp *op, int ret)
         s->buf_free_count++;
     }

-    sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
-    chunk_num = op->sector_num / sectors_per_chunk;
-    nb_chunks = DIV_ROUND_UP(op->nb_sectors, sectors_per_chunk);
+    chunk_num = op->offset / s->granularity;
+    nb_chunks = DIV_ROUND_UP(op->bytes, s->granularity);
     bitmap_clear(s->in_flight_bitmap, chunk_num, nb_chunks);
     if (ret >= 0) {
         if (s->cow_bitmap) {
             bitmap_set(s->cow_bitmap, chunk_num, nb_chunks);
         }
         if (!s->initial_zeroing_ongoing) {
-            s->common.offset += (uint64_t)op->nb_sectors * BDRV_SECTOR_SIZE;
+            s->common.offset += op->bytes;
         }
     }
     qemu_iovec_destroy(&op->qiov);
@@ -144,7 +141,8 @@ static void mirror_write_complete(void *opaque, int ret)
     if (ret < 0) {
         BlockErrorAction action;

-        bdrv_set_dirty_bitmap(s->dirty_bitmap, op->sector_num, op->nb_sectors);
+        bdrv_set_dirty_bitmap(s->dirty_bitmap, op->offset >> BDRV_SECTOR_BITS,
+                              op->bytes >> BDRV_SECTOR_BITS);
         action = mirror_error_action(s, false, -ret);
         if (action == BLOCK_ERROR_ACTION_REPORT && s->ret >= 0) {
             s->ret = ret;
@@ -163,7 +161,8 @@ static void mirror_read_complete(void *opaque, int ret)
     if (ret < 0) {
         BlockErrorAction action;

-        bdrv_set_dirty_bitmap(s->dirty_bitmap, op->sector_num, op->nb_sectors);
+        bdrv_set_dirty_bitmap(s->dirty_bitmap, op->offset >> BDRV_SECTOR_BITS,
+                              op->bytes >> BDRV_SECTOR_BITS);
         action = mirror_error_action(s, true, -ret);
         if (action == BLOCK_ERROR_ACTION_REPORT && s->ret >= 0) {
             s->ret = ret;
@@ -171,7 +170,7 @@ static void mirror_read_complete(void *opaque, int ret)

         mirror_iteration_done(op, ret);
     } else {
-        blk_aio_pwritev(s->target, op->sector_num * BDRV_SECTOR_SIZE, &op->qiov,
+        blk_aio_pwritev(s->target, op->offset, &op->qiov,
                         0, mirror_write_complete, op);
     }
     aio_context_release(blk_get_aio_context(s->common.blk));
@@ -211,7 +210,8 @@ static int mirror_cow_align(MirrorBlockJob *s,
         align_nb_sectors = max_sectors;
         if (need_cow) {
             align_nb_sectors = QEMU_ALIGN_DOWN(align_nb_sectors,
-                                               s->target_cluster_sectors);
+                                               s->target_cluster_size >>
+                                               BDRV_SECTOR_BITS);
         }
     }
     /* Clipping may result in align_nb_sectors unaligned to chunk boundary, but
@@ -277,8 +277,8 @@ static int mirror_do_read(MirrorBlockJob *s, int64_t sector_num,
     /* Allocate a MirrorOp that is used as an AIO callback.  */
     op = g_new(MirrorOp, 1);
     op->s = s;
-    op->sector_num = sector_num;
-    op->nb_sectors = nb_sectors;
+    op->offset = sector_num * BDRV_SECTOR_SIZE;
+    op->bytes = nb_sectors * BDRV_SECTOR_SIZE;

     /* Now make a QEMUIOVector taking enough granularity-sized chunks
      * from s->buf_free.
@@ -295,7 +295,7 @@ static int mirror_do_read(MirrorBlockJob *s, int64_t sector_num,

     /* Copy the dirty cluster.  */
     s->in_flight++;
-    s->sectors_in_flight += nb_sectors;
+    s->bytes_in_flight += nb_sectors * BDRV_SECTOR_SIZE;
     trace_mirror_one_iteration(s, sector_num * BDRV_SECTOR_SIZE,
                                nb_sectors * BDRV_SECTOR_SIZE);

@@ -315,19 +315,17 @@ static void mirror_do_zero_or_discard(MirrorBlockJob *s,
      * so the freeing in mirror_iteration_done is nop. */
     op = g_new0(MirrorOp, 1);
     op->s = s;
-    op->sector_num = sector_num;
-    op->nb_sectors = nb_sectors;
+    op->offset = sector_num * BDRV_SECTOR_SIZE;
+    op->bytes = nb_sectors * BDRV_SECTOR_SIZE;

     s->in_flight++;
-    s->sectors_in_flight += nb_sectors;
+    s->bytes_in_flight += nb_sectors * BDRV_SECTOR_SIZE;
     if (is_discard) {
         blk_aio_pdiscard(s->target, sector_num << BDRV_SECTOR_BITS,
-                         op->nb_sectors << BDRV_SECTOR_BITS,
-                         mirror_write_complete, op);
+                         op->bytes, mirror_write_complete, op);
     } else {
         blk_aio_pwrite_zeroes(s->target, sector_num * BDRV_SECTOR_SIZE,
-                              op->nb_sectors * BDRV_SECTOR_SIZE,
-                              s->unmap ? BDRV_REQ_MAY_UNMAP : 0,
+                              op->bytes, s->unmap ? BDRV_REQ_MAY_UNMAP : 0,
                               mirror_write_complete, op);
     }
 }
@@ -342,8 +340,7 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
     int64_t end = s->bdev_length / BDRV_SECTOR_SIZE;
     int sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
     bool write_zeroes_ok = bdrv_can_write_zeroes_with_unmap(blk_bs(s->target));
-    int max_io_sectors = MAX((s->buf_size >> BDRV_SECTOR_BITS) / MAX_IN_FLIGHT,
-                             MAX_IO_SECTORS);
+    int max_io_bytes = MAX(s->buf_size / MAX_IN_FLIGHT, MAX_IO_BYTES);

     sector_num = bdrv_dirty_iter_next(s->dbi);
     if (sector_num < 0) {
@@ -410,9 +407,10 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
                                           nb_chunks * sectors_per_chunk,
                                           &io_sectors, &file);
         if (ret < 0) {
-            io_sectors = MIN(nb_chunks * sectors_per_chunk, max_io_sectors);
+            io_sectors = MIN(nb_chunks * sectors_per_chunk,
+                             max_io_bytes >> BDRV_SECTOR_BITS);
         } else if (ret & BDRV_BLOCK_DATA) {
-            io_sectors = MIN(io_sectors, max_io_sectors);
+            io_sectors = MIN(io_sectors, max_io_bytes >> BDRV_SECTOR_BITS);
         }

         io_sectors -= io_sectors % sectors_per_chunk;
@@ -707,7 +705,6 @@ static void coroutine_fn mirror_run(void *opaque)
     char backing_filename[2]; /* we only need 2 characters because we are only
                                  checking for a NULL string */
     int ret = 0;
-    int target_cluster_size = BDRV_SECTOR_SIZE;

     if (block_job_is_cancelled(&s->common)) {
         goto immediate_exit;
@@ -756,17 +753,17 @@ static void coroutine_fn mirror_run(void *opaque)
      * the destination do COW.  Instead, we copy sectors around the
      * dirty data if needed.  We need a bitmap to do that.
      */
+    s->target_cluster_size = BDRV_SECTOR_SIZE;
     bdrv_get_backing_filename(target_bs, backing_filename,
                               sizeof(backing_filename));
     if (!bdrv_get_info(target_bs, &bdi) && bdi.cluster_size) {
-        target_cluster_size = bdi.cluster_size;
+        s->target_cluster_size = bdi.cluster_size;
     }
     if (backing_filename[0] && !target_bs->backing
-        && s->granularity < target_cluster_size) {
-        s->buf_size = MAX(s->buf_size, target_cluster_size);
+        && s->granularity < s->target_cluster_size) {
+        s->buf_size = MAX(s->buf_size, s->target_cluster_size);
         s->cow_bitmap = bitmap_new(length);
     }
-    s->target_cluster_sectors = target_cluster_size >> BDRV_SECTOR_BITS;
     s->max_iov = MIN(bs->bl.max_iov, target_bs->bl.max_iov);

     s->buf = qemu_try_blockalign(bs, s->buf_size);
@@ -802,10 +799,10 @@ static void coroutine_fn mirror_run(void *opaque)
         cnt = bdrv_get_dirty_count(s->dirty_bitmap);
         /* s->common.offset contains the number of bytes already processed so
          * far, cnt is the number of dirty sectors remaining and
-         * s->sectors_in_flight is the number of sectors currently being
+         * s->bytes_in_flight is the number of bytes currently being
          * processed; together those are the current total operation length */
-        s->common.len = s->common.offset +
-                        (cnt + s->sectors_in_flight) * BDRV_SECTOR_SIZE;
+        s->common.len = s->common.offset + s->bytes_in_flight +
+            cnt * BDRV_SECTOR_SIZE;

         /* Note that even when no rate limit is applied we need to yield
          * periodically with no pending I/O so that bdrv_drain_all() returns.
