diff --git a/block/mirror.c b/block/mirror.c
index 69a1a7cc96..d6034f5b70 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -23,7 +23,9 @@
 
 #define SLICE_TIME    100000000ULL /* ns */
 #define MAX_IN_FLIGHT 16
-#define DEFAULT_MIRROR_BUF_SIZE   (10 << 20)
+#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)
 
 /* The mirroring buffer is a list of granularity-sized chunks.
  * Free chunks are organized in a list.
@@ -325,6 +327,8 @@ 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);
 
     sector_num = hbitmap_iter_next(&s->hbi);
     if (sector_num < 0) {
@@ -388,7 +392,9 @@ static uint64_t coroutine_fn mirror_iteration(MirrorBlockJob *s)
                                           nb_chunks * sectors_per_chunk,
                                           &io_sectors, &file);
         if (ret < 0) {
-            io_sectors = nb_chunks * sectors_per_chunk;
+            io_sectors = MIN(nb_chunks * sectors_per_chunk, max_io_sectors);
+        } else if (ret & BDRV_BLOCK_DATA) {
+            io_sectors = MIN(io_sectors, max_io_sectors);
         }
 
         io_sectors -= io_sectors % sectors_per_chunk;
diff --git a/qapi/block-core.json b/qapi/block-core.json
index d4bab5d991..2bbc027311 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1692,9 +1692,9 @@
 # Drivers that are supported in block device operations.
 #
 # @host_device, @host_cdrom: Since 2.1
+# @gluster: Since 2.7
 #
 # Since: 2.0
-# @gluster: Since 2.7
 ##
 { 'enum': 'BlockdevDriver',
   'data': [ 'archipelago', 'blkdebug', 'blkverify', 'bochs', 'cloop',
@@ -2138,7 +2138,7 @@
 #
 # @path:        absolute path to image file in gluster volume
 #
-# @server:      gluster server description
+# @server:      gluster servers description
 #
 # @debug-level: #optional libgfapi log level (default '4' which is Error)
 #
@@ -2148,7 +2148,7 @@
   'data': { 'volume': 'str',
             'path': 'str',
             'server': ['GlusterServer'],
-            '*debug_level': 'int' } }
+            '*debug-level': 'int' } }
 
 ##
 # @BlockdevOptions