diff --git a/block/vmdk.c b/block/vmdk.c
index 73ae786..e5a289d 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -136,6 +136,7 @@ typedef struct VmdkMetaData {
     unsigned int l2_offset;
     int valid;
     uint32_t *l2_cache_entry;
+    uint32_t nb_clusters;
 } VmdkMetaData;
 
 typedef struct VmdkGrainMarker {
@@ -254,6 +255,14 @@ static inline uint64_t vmdk_find_offset_in_cluster(VmdkExtent *extent,
     return extent_relative_offset % cluster_size;
 }
 
+static inline uint64_t size_to_clusters(VmdkExtent *extent, uint64_t size)
+{
+    uint64_t cluster_size, round_off_size;
+    cluster_size = extent->cluster_sectors * BDRV_SECTOR_SIZE;
+    round_off_size = cluster_size - (size % cluster_size);
+    return DIV_ROUND_UP(size + round_off_size, BDRV_SECTOR_SIZE * 128) - 1;
+}
+
 static uint32_t vmdk_read_cid(BlockDriverState *bs, int parent)
 {
     char *desc;
@@ -1028,6 +1037,133 @@ static void vmdk_refresh_limits(BlockDriverState *bs, Error **errp)
     }
 }
 
+static int vmdk_L2update(VmdkExtent *extent, VmdkMetaData *m_data,
+                         uint32_t offset)
+{
+    offset = cpu_to_le32(offset);
+    /* update L2 table */
+    if (bdrv_pwrite_sync(extent->file,
+                ((int64_t)m_data->l2_offset * 512)
+                    + (m_data->l2_index * sizeof(offset)),
+                &offset, sizeof(offset)) < 0) {
+        return VMDK_ERROR;
+    }
+    /* update backup L2 table */
+    if (extent->l1_backup_table_offset != 0) {
+        m_data->l2_offset = extent->l1_backup_table[m_data->l1_index];
+        if (bdrv_pwrite_sync(extent->file,
+                    ((int64_t)m_data->l2_offset * 512)
+                        + (m_data->l2_index * sizeof(offset)),
+                    &offset, sizeof(offset)) < 0) {
+            return VMDK_ERROR;
+        }
+    }
+    if (m_data->l2_cache_entry) {
+        *m_data->l2_cache_entry = offset;
+    }
+
+    return VMDK_OK;
+}
+
+/*
+ * vmdk_l2load
+ *
+ * Loads a new L2 table into memory. If the table is in the cache, the cache
+ * is used; otherwise the L2 table is loaded from the image file.
+ *
+ * Returns:
+ *   VMDK_OK:       on success
+ *   VMDK_ERROR:    in error cases
+ */
+static int vmdk_l2load(VmdkExtent *extent, uint64_t offset, int l2_offset,
+                       uint32_t **new_l2_table, int *new_l2_index)
+{
+    int min_index, i, j;
+    uint32_t *l2_table;
+    uint32_t min_count;
+
+    for (i = 0; i < L2_CACHE_SIZE; i++) {
+        if (l2_offset == extent->l2_cache_offsets[i]) {
+            /* increment the hit count */
+            if (++extent->l2_cache_counts[i] == UINT32_MAX) {
+                for (j = 0; j < L2_CACHE_SIZE; j++) {
+                    extent->l2_cache_counts[j] >>= 1;
+                }
+            }
+            l2_table = extent->l2_cache + (i * extent->l2_size);
+            goto found;
+        }
+    }
+    /* not found: load a new entry in the least used one */
+    min_index = 0;
+    min_count = UINT32_MAX;
+    for (i = 0; i < L2_CACHE_SIZE; i++) {
+        if (extent->l2_cache_counts[i] < min_count) {
+            min_count = extent->l2_cache_counts[i];
+            min_index = i;
+        }
+    }
+    l2_table = extent->l2_cache + (min_index * extent->l2_size);
+    if (bdrv_pread(extent->file,
+                (int64_t)l2_offset * 512,
+                l2_table,
+                extent->l2_size * sizeof(uint32_t)
+            ) != extent->l2_size * sizeof(uint32_t)) {
+        return VMDK_ERROR;
+    }
+
+    extent->l2_cache_offsets[min_index] = l2_offset;
+    extent->l2_cache_counts[min_index] = 1;
+found:
+    *new_l2_index = ((offset >> 9) / extent->cluster_sectors) % extent->l2_size;
+    *new_l2_table = l2_table;
+
+    return VMDK_OK;
+}
+
+/*
+ * get_cluster_table
+ *
+ * for a given offset, load (and allocate if needed) the l2 table.
+ *
+ * Returns:
+ *   VMDK_OK:        on success
+ *
+ *   VMDK_UNALLOC:   if cluster is not mapped
+ *
+ *   VMDK_ERROR:     in error cases
+ */
+static int get_cluster_table(VmdkExtent *extent, uint64_t offset,
+                             int *new_l1_index, int *new_l2_offset,
+                             int *new_l2_index, uint32_t **new_l2_table)
+{
+    int l1_index, l2_offset, l2_index;
+    uint32_t *l2_table;
+    int ret;
+
+    offset -= (extent->end_sector - extent->sectors) * SECTOR_SIZE;
+    l1_index = (offset >> 9) / extent->l1_entry_sectors;
+    if (l1_index >= extent->l1_size) {
+        return VMDK_ERROR;
+    }
+    l2_offset = extent->l1_table[l1_index];
+    if (!l2_offset) {
+        return VMDK_UNALLOC;
+    }
+
+    ret = vmdk_l2load(extent, offset, l2_offset, &l2_table, &l2_index);
+    if (ret < 0) {
+        return ret;
+    }
+
+    *new_l1_index = l1_index;
+    *new_l2_offset = l2_offset;
+    *new_l2_index = l2_index;
+    *new_l2_table = l2_table;
+
+    return VMDK_OK;
+}
+
 /*
  * vmdk_perform_cow
  *
@@ -1115,29 +1251,168 @@ exit:
     return ret;
 }
 
-static int vmdk_L2update(VmdkExtent *extent, VmdkMetaData *m_data,
-                         uint32_t offset)
+/*
+ * handle_alloc
+ *
+ * Allocates new clusters for an area that either is yet unallocated or needs a
+ * copy on write. If *cluster_offset is non_zero, clusters are only allocated if
+ * the new allocation can match the specified host offset.
+ *
+ * Returns:
+ *   VMDK_OK:       if new clusters were allocated, *bytes may be decreased if
+ *                  the new allocation doesn't cover all of the requested area.
+ *                  *cluster_offset is updated to contain the offset of the
+ *                  first newly allocated cluster.
+ *
+ *   VMDK_UNALLOC:  if no clusters could be allocated. *cluster_offset is left
+ *                  unchanged.
+ *
+ *   VMDK_ERROR:    in error cases
+ */
+static int handle_alloc(BlockDriverState *bs, VmdkExtent *extent,
+                        uint64_t offset, uint64_t *cluster_offset,
+                        int64_t *bytes, VmdkMetaData *m_data,
+                        bool allocate, uint32_t *total_alloc_clusters)
 {
-    offset = cpu_to_le32(offset);
-    /* update L2 table */
-    if (bdrv_pwrite_sync(extent->file,
-                ((int64_t)m_data->l2_offset * 512)
-                    + (m_data->l2_index * sizeof(offset)),
-                &offset, sizeof(offset)) < 0) {
-        return VMDK_ERROR;
+    int l1_index, l2_offset, l2_index;
+    uint32_t *l2_table;
+    uint32_t cluster_sector;
+    uint32_t nb_clusters;
+    bool zeroed = false;
+    uint64_t skip_start_bytes, skip_end_bytes;
+    int ret;
+
+    ret = get_cluster_table(extent, offset, &l1_index, &l2_offset,
+                            &l2_index, &l2_table);
+    if (ret < 0) {
+        return ret;
     }
-    /* update backup L2 table */
-    if (extent->l1_backup_table_offset != 0) {
-        m_data->l2_offset = extent->l1_backup_table[m_data->l1_index];
-        if (bdrv_pwrite_sync(extent->file,
-                    ((int64_t)m_data->l2_offset * 512)
-                        + (m_data->l2_index * sizeof(offset)),
-                    &offset, sizeof(offset)) < 0) {
-            return VMDK_ERROR;
+
+    cluster_sector = le32_to_cpu(l2_table[l2_index]);
+
+    skip_start_bytes = vmdk_find_offset_in_cluster(extent, offset);
+    /* Calculate the number of clusters to look for. Here it will return one
+     * cluster less than the actual value calculated as we may need to perfrom
+     * COW for the last one. */
+    nb_clusters = size_to_clusters(extent, skip_start_bytes + *bytes);
+
+    nb_clusters = MIN(nb_clusters, extent->l2_size - l2_index);
+    assert(nb_clusters <= INT_MAX);
+
+    /* update bytes according to final nb_clusters value */
+    if (nb_clusters != 0) {
+        *bytes = ((nb_clusters * extent->cluster_sectors) << 9)
+                                            - skip_start_bytes;
+    } else {
+        nb_clusters = 1;
+    }
+    *total_alloc_clusters += nb_clusters;
+    skip_end_bytes = skip_start_bytes + MIN(*bytes,
+                     extent->cluster_sectors * BDRV_SECTOR_SIZE
+                                    - skip_start_bytes);
+
+    if (extent->has_zero_grain && cluster_sector == VMDK_GTE_ZEROED) {
+        zeroed = true;
+    }
+
+    if (!cluster_sector || zeroed) {
+        if (!allocate) {
+            return zeroed ? VMDK_ZEROED : VMDK_UNALLOC;
+        }
+
+        cluster_sector = extent->next_cluster_sector;
+        extent->next_cluster_sector += extent->cluster_sectors
+                                                * nb_clusters;
+
+        ret = vmdk_perform_cow(bs, extent, cluster_sector * BDRV_SECTOR_SIZE,
+                               offset, skip_start_bytes,
+                               skip_end_bytes);
+        if (ret < 0) {
+            return ret;
+        }
+        if (m_data) {
+            m_data->valid = 1;
+            m_data->l1_index = l1_index;
+            m_data->l2_index = l2_index;
+            m_data->l2_offset = l2_offset;
+            m_data->l2_cache_entry = &l2_table[l2_index];
+            m_data->nb_clusters = nb_clusters;
         }
     }
-    if (m_data->l2_cache_entry) {
-        *m_data->l2_cache_entry = offset;
+    *cluster_offset = cluster_sector << BDRV_SECTOR_BITS;
+    return VMDK_OK;
+}
+
+/*
+ * vmdk_alloc_cluster_offset
+ *
+ * For a given offset on the virtual disk, find the cluster offset in vmdk
+ * file. If the offset is not found, allocate a new cluster.
+ *
+ * If the cluster is newly allocated, m_data->nb_clusters is set to the number
+ * of contiguous clusters that have been allocated. In this case, the other
+ * fields of m_data are valid and contain information about the first allocated
+ * cluster.
+ *
+ * Returns:
+ *
+ *   VMDK_OK:           on success and @cluster_offset was set
+ *
+ *   VMDK_UNALLOC:      if no clusters were allocated and @cluster_offset is
+ *                      set to zero
+ *
+ *   VMDK_ERROR:        in error cases
+ */
+static int vmdk_alloc_cluster_offset(BlockDriverState *bs,
+                                     VmdkExtent *extent,
+                                     VmdkMetaData *m_data, uint64_t offset,
+                                     bool allocate, uint64_t *cluster_offset,
+                                     int64_t bytes,
+                                     uint32_t *total_alloc_clusters)
+{
+    uint64_t start, remaining;
+    uint64_t new_cluster_offset;
+    int64_t n_bytes;
+    int ret;
+
+    if (extent->flat) {
+        *cluster_offset = extent->flat_start_offset;
+        return VMDK_OK;
+    }
+
+    start = offset;
+    remaining = bytes;
+    new_cluster_offset = 0;
+    *cluster_offset = 0;
+    n_bytes = 0;
+    if (m_data) {
+        m_data->valid = 0;
+    }
+
+    /* due to L2 table margins all bytes may not get allocated at once */
+    while (true) {
+
+        if (!*cluster_offset) {
+            *cluster_offset = new_cluster_offset;
+        }
+
+        start              += n_bytes;
+        remaining          -= n_bytes;
+        new_cluster_offset += n_bytes;
+
+        if (remaining == 0) {
+            break;
+        }
+
+        n_bytes = remaining;
+
+        ret = handle_alloc(bs, extent, start, &new_cluster_offset, &n_bytes,
+                           m_data, allocate, total_alloc_clusters);
+
+        if (ret < 0) {
+            return ret;
+
+        }
     }
 
     return VMDK_OK;
@@ -1567,6 +1842,7 @@ static int vmdk_pwritev(BlockDriverState *bs, uint64_t offset,
     uint64_t cluster_offset;
     uint64_t bytes_done = 0;
     VmdkMetaData m_data;
+    uint32_t total_alloc_clusters = 0;
 
     if (DIV_ROUND_UP(offset, BDRV_SECTOR_SIZE) > bs->total_sectors) {
         error_report("Wrong offset: offset=0x%" PRIx64
@@ -1584,10 +1860,10 @@ static int vmdk_pwritev(BlockDriverState *bs, uint64_t offset,
         n_bytes = MIN(bytes, extent->cluster_sectors * BDRV_SECTOR_SIZE
                              - offset_in_cluster);
 
-        ret = get_cluster_offset(bs, extent, &m_data, offset,
-                                 !(extent->compressed || zeroed),
-                                 &cluster_offset, offset_in_cluster,
-                                 offset_in_cluster + n_bytes);
+        ret = vmdk_alloc_cluster_offset(bs, extent, &m_data, offset,
+                                        !(extent->compressed || zeroed),
+                                        &cluster_offset, n_bytes,
+                                        &total_alloc_clusters);
         if (extent->compressed) {
             if (ret == VMDK_OK) {
                 /* Refuse write to allocated cluster for streamOptimized */
@@ -1596,19 +1872,22 @@ static int vmdk_pwritev(BlockDriverState *bs, uint64_t offset,
                 return -EIO;
             } else {
                 /* allocate */
-                ret = get_cluster_offset(bs, extent, &m_data, offset,
-                                         true, &cluster_offset, 0, 0);
+                ret = vmdk_alloc_cluster_offset(bs, extent, &m_data, offset,
+                                        true, &cluster_offset, n_bytes,
+                                        &total_alloc_clusters);
             }
         }
         if (ret == VMDK_ERROR) {
             return -EINVAL;
         }
+
         if (zeroed) {
             /* Do zeroed write, buf is ignored */
-            if (extent->has_zero_grain &&
-                    offset_in_cluster == 0 &&
-                    n_bytes >= extent->cluster_sectors * BDRV_SECTOR_SIZE) {
-                n_bytes = extent->cluster_sectors * BDRV_SECTOR_SIZE;
+            if (extent->has_zero_grain && offset_in_cluster == 0 &&
+                    n_bytes >= extent->cluster_sectors * BDRV_SECTOR_SIZE *
+                        total_alloc_clusters) {
+                n_bytes = extent->cluster_sectors * BDRV_SECTOR_SIZE *
+                                        total_alloc_clusters;
                 if (!zero_dry_run) {
                     /* update L2 tables */
                     if (vmdk_L2update(extent, &m_data, VMDK_GTE_ZEROED)
