diff --git a/hw/block/block.c b/hw/block/block.c
index a625773d442cf4bd16263e0549fe91602550ecc9..f7243e5b948fddda88fda8f51f7f7b490ef7f704 100644
--- a/hw/block/block.c
+++ b/hw/block/block.c
@@ -25,6 +25,30 @@ void blkconf_serial(BlockConf *conf, char **serial)
     }
 }
 
+void blkconf_blocksizes(BlockConf *conf)
+{
+    BlockBackend *blk = conf->blk;
+    BlockSizes blocksizes;
+    int backend_ret;
+
+    backend_ret = blk_probe_blocksizes(blk, &blocksizes);
+    /* fill in detected values if they are not defined via qemu command line */
+    if (!conf->physical_block_size) {
+        if (!backend_ret) {
+           conf->physical_block_size = blocksizes.phys;
+        } else {
+            conf->physical_block_size = BDRV_SECTOR_SIZE;
+        }
+    }
+    if (!conf->logical_block_size) {
+        if (!backend_ret) {
+            conf->logical_block_size = blocksizes.log;
+        } else {
+            conf->logical_block_size = BDRV_SECTOR_SIZE;
+        }
+    }
+}
+
 void blkconf_geometry(BlockConf *conf, int *ptrans,
                       unsigned cyls_max, unsigned heads_max, unsigned secs_max,
                       Error **errp)
diff --git a/hw/block/hd-geometry.c b/hw/block/hd-geometry.c
index 6fcf74df44fcdae964e87ad7afca6240e55c3b48..b187878facfc7199eb15c90cd4547a51713b8d02 100644
--- a/hw/block/hd-geometry.c
+++ b/hw/block/hd-geometry.c
@@ -121,8 +121,16 @@ void hd_geometry_guess(BlockBackend *blk,
                        int *ptrans)
 {
     int cylinders, heads, secs, translation;
+    HDGeometry geo;
 
-    if (guess_disk_lchs(blk, &cylinders, &heads, &secs) < 0) {
+    /* Try to probe the backing device geometry, otherwise fallback
+       to the old logic. (as of 12/2014 probing only succeeds on DASDs) */
+    if (blk_probe_geometry(blk, &geo) == 0) {
+        *pcyls = geo.cylinders;
+        *psecs = geo.sectors;
+        *pheads = geo.heads;
+        translation = BIOS_ATA_TRANSLATION_NONE;
+    } else if (guess_disk_lchs(blk, &cylinders, &heads, &secs) < 0) {
         /* no LCHS guess: use a standard physical disk geometry  */
         guess_chs_for_size(blk, pcyls, pheads, psecs);
         translation = hd_bios_chs_auto_trans(*pcyls, *pheads, *psecs);
diff --git a/hw/block/nvme.c b/hw/block/nvme.c
index ce079aefdd615ac1e0e6db3e970c38706c91307c..0f3dfb90ea65c88a5e2db4a5aae5cd9cdeee9967 100644
--- a/hw/block/nvme.c
+++ b/hw/block/nvme.c
@@ -765,6 +765,7 @@ static int nvme_init(PCIDevice *pci_dev)
     if (!n->serial) {
         return -1;
     }
+    blkconf_blocksizes(&n->conf);
 
     pci_conf = pci_dev->config;
     pci_conf[PCI_INTERRUPT_PIN] = 1;
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 3ad5fe44e2adfd54726dd9d28969819d8d54592a..2acfef87eba29768599269b33a31b228e70f89bd 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -893,6 +893,7 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
         error_propagate(errp, err);
         return;
     }
+    blkconf_blocksizes(&conf->conf);
 
     virtio_init(vdev, "virtio-blk", VIRTIO_ID_BLOCK,
                 sizeof(struct virtio_blk_config));
diff --git a/hw/core/qdev-properties.c b/hw/core/qdev-properties.c
index 2e47f70eb435f4e431fe850d0ddcf69a847bd606..ba8170914256142d183443798758454f87993972 100644
--- a/hw/core/qdev-properties.c
+++ b/hw/core/qdev-properties.c
@@ -580,7 +580,8 @@ static void set_blocksize(Object *obj, Visitor *v, void *opaque,
         error_propagate(errp, local_err);
         return;
     }
-    if (value < min || value > max) {
+    /* value of 0 means "unset" */
+    if (value && (value < min || value > max)) {
         error_set(errp, QERR_PROPERTY_VALUE_OUT_OF_RANGE,
                   dev->id?:"", name, (int64_t)value, min, max);
         return;
diff --git a/hw/ide/qdev.c b/hw/ide/qdev.c
index b4103fa009bcc31e8ea7fdddc8f133afc212b90d..788b36133c04fa75b4f98cdbead66c720fd5554c 100644
--- a/hw/ide/qdev.c
+++ b/hw/ide/qdev.c
@@ -163,6 +163,7 @@ static int ide_dev_initfn(IDEDevice *dev, IDEDriveKind kind)
         return -1;
     }
 
+    blkconf_blocksizes(&dev->conf);
     if (dev->conf.logical_block_size != 512) {
         error_report("logical_block_size must be 512 for IDE");
         return -1;
diff --git a/hw/scsi/scsi-disk.c b/hw/scsi/scsi-disk.c
index f65618d80245a95035bbbfa0920ba9d7a08d4888..2921728be45a3481e82706b3faa659651086e8c5 100644
--- a/hw/scsi/scsi-disk.c
+++ b/hw/scsi/scsi-disk.c
@@ -2251,6 +2251,7 @@ static void scsi_realize(SCSIDevice *dev, Error **errp)
     }
 
     blkconf_serial(&s->qdev.conf, &s->serial);
+    blkconf_blocksizes(&s->qdev.conf);
     if (dev->type == TYPE_DISK) {
         blkconf_geometry(&dev->conf, NULL, 65535, 255, 255, &err);
         if (err) {
@@ -2290,6 +2291,7 @@ static void scsi_realize(SCSIDevice *dev, Error **errp)
 static void scsi_hd_realize(SCSIDevice *dev, Error **errp)
 {
     SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, dev);
+    blkconf_blocksizes(&s->qdev.conf);
     s->qdev.blocksize = s->qdev.conf.logical_block_size;
     s->qdev.type = TYPE_DISK;
     if (!s->product) {
diff --git a/hw/usb/dev-storage.c b/hw/usb/dev-storage.c
index 65d9aa6147c4c2f4597f6e5feade85910eea49a5..8edc314fab5dbcf0ae411b3777fd2e818cacc993 100644
--- a/hw/usb/dev-storage.c
+++ b/hw/usb/dev-storage.c
@@ -611,6 +611,7 @@ static void usb_msd_realize_storage(USBDevice *dev, Error **errp)
     }
 
     blkconf_serial(&s->conf, &dev->serial);
+    blkconf_blocksizes(&s->conf);
 
     /*
      * Hack alert: this pretends to be a block device, but it's really
diff --git a/include/hw/block/block.h b/include/hw/block/block.h
index 0d0ce9a4676309478b889df9e531c6920925d626..8d7c4b413f26edcc2141979e48a813ffccb1c903 100644
--- a/include/hw/block/block.h
+++ b/include/hw/block/block.h
@@ -44,9 +44,9 @@ static inline unsigned int get_physical_block_exp(BlockConf *conf)
 #define DEFINE_BLOCK_PROPERTIES(_state, _conf)                          \
     DEFINE_PROP_DRIVE("drive", _state, _conf.blk),                      \
     DEFINE_PROP_BLOCKSIZE("logical_block_size", _state,                 \
-                          _conf.logical_block_size, 512),               \
+                          _conf.logical_block_size),                    \
     DEFINE_PROP_BLOCKSIZE("physical_block_size", _state,                \
-                          _conf.physical_block_size, 512),              \
+                          _conf.physical_block_size),                   \
     DEFINE_PROP_UINT16("min_io_size", _state, _conf.min_io_size, 0),  \
     DEFINE_PROP_UINT32("opt_io_size", _state, _conf.opt_io_size, 0),    \
     DEFINE_PROP_UINT32("discard_granularity", _state, \
@@ -63,6 +63,7 @@ void blkconf_serial(BlockConf *conf, char **serial);
 void blkconf_geometry(BlockConf *conf, int *trans,
                       unsigned cyls_max, unsigned heads_max, unsigned secs_max,
                       Error **errp);
+void blkconf_blocksizes(BlockConf *conf);
 
 /* Hard disk geometry */
 
diff --git a/include/hw/qdev-properties.h b/include/hw/qdev-properties.h
index 070006c71561b495be8d0ed7258f3e127b9a5df5..2fdcbce0329d9565ca36aacb3b63333cbed8fdf7 100644
--- a/include/hw/qdev-properties.h
+++ b/include/hw/qdev-properties.h
@@ -149,8 +149,8 @@ extern PropertyInfo qdev_prop_arraylen;
                         LostTickPolicy)
 #define DEFINE_PROP_BIOS_CHS_TRANS(_n, _s, _f, _d) \
     DEFINE_PROP_DEFAULT(_n, _s, _f, _d, qdev_prop_bios_chs_trans, int)
-#define DEFINE_PROP_BLOCKSIZE(_n, _s, _f, _d) \
-    DEFINE_PROP_DEFAULT(_n, _s, _f, _d, qdev_prop_blocksize, uint16_t)
+#define DEFINE_PROP_BLOCKSIZE(_n, _s, _f) \
+    DEFINE_PROP_DEFAULT(_n, _s, _f, 0, qdev_prop_blocksize, uint16_t)
 #define DEFINE_PROP_PCI_HOST_DEVADDR(_n, _s, _f) \
     DEFINE_PROP(_n, _s, _f, qdev_prop_pci_host_devaddr, PCIHostDeviceAddress)