diff --git a/block-qcow2.c b/block-qcow2.c
index c9d68af93f..b3b5f8f090 100644
--- a/block-qcow2.c
+++ b/block-qcow2.c
@@ -189,6 +189,14 @@ static int qcow_open(BlockDriverState *bs, const char *filename, int flags)
     int len, i, shift, ret;
     QCowHeader header;
 
+    /* Performance is terrible right now with cache=writethrough due mainly
+     * to reference count updates.  If the user does not explicitly specify
+     * a caching type, force to writeback caching.
+     */
+    if ((flags & BDRV_O_CACHE_DEF)) {
+        flags |= BDRV_O_CACHE_WB;
+        flags &= ~BDRV_O_CACHE_DEF;
+    }
     ret = bdrv_file_open(&s->hd, filename, flags);
     if (ret < 0)
         return ret;
diff --git a/block.h b/block.h
index 99d3a1e17b..c3314a1dbe 100644
--- a/block.h
+++ b/block.h
@@ -49,8 +49,9 @@ typedef struct QEMUSnapshotInfo {
                                      bdrv_file_open()) */
 #define BDRV_O_NOCACHE     0x0020 /* do not use the host page cache */
 #define BDRV_O_CACHE_WB    0x0040 /* use write-back caching */
+#define BDRV_O_CACHE_DEF   0x0080 /* use default caching */
 
-#define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_CACHE_WB)
+#define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_CACHE_WB | BDRV_O_CACHE_DEF)
 
 void bdrv_info(void);
 void bdrv_info_stats(void);
diff --git a/qemu-doc.texi b/qemu-doc.texi
index f2c56ce0e0..77170d3ad6 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -289,6 +289,12 @@ The host page can be avoided entirely with @option{cache=none}.  This will
 attempt to do disk IO directly to the guests memory.  QEMU may still perform
 an internal copy of the data.
 
+Some block drivers perform badly with @option{cache=writethrough}, most notably,
+qcow2.  If performance is more important than correctness,
+@option{cache=writeback} should be used with qcow2.  By default, if no explicit
+caching is specified for a qcow2 disk image, @option{cache=writeback} will be
+used.  For all other disk types, @option{cache=writethrough} is the default.
+
 Instead of @option{-cdrom} you can use:
 @example
 qemu -drive file=file,index=2,media=cdrom
diff --git a/vl.c b/vl.c
index 1cee2a793f..00adb79978 100644
--- a/vl.c
+++ b/vl.c
@@ -2242,7 +2242,7 @@ static int drive_init(struct drive_opt *arg, int snapshot,
     unit_id = -1;
     translation = BIOS_ATA_TRANSLATION_AUTO;
     index = -1;
-    cache = 1;
+    cache = 3;
 
     if (machine->use_scsi) {
         type = IF_SCSI;
@@ -2517,6 +2517,8 @@ static int drive_init(struct drive_opt *arg, int snapshot,
         bdrv_flags |= BDRV_O_NOCACHE;
     else if (cache == 2) /* write-back */
         bdrv_flags |= BDRV_O_CACHE_WB;
+    else if (cache == 3) /* not specified */
+        bdrv_flags |= BDRV_O_CACHE_DEF;
     if (bdrv_open2(bdrv, file, bdrv_flags, drv) < 0 || qemu_key_check(bdrv, file)) {
         fprintf(stderr, "qemu: could not open disk image %s\n",
                         file);