diff --git a/port/android/storage.c b/port/android/storage.c
index 58fdae331c..ed2788905a 100644
--- a/port/android/storage.c
+++ b/port/android/storage.c
@@ -90,8 +90,8 @@ oc_storage_reset(void)
   return 0;
 }
 
-long
-oc_storage_read(const char *store, uint8_t *buf, size_t size)
+static int
+storage_open(const char *store, FILE **fp)
 {
   if (g_store_path_len == 0) {
     return -ENOENT;
@@ -105,10 +105,44 @@ oc_storage_read(const char *store, uint8_t *buf, size_t size)
   memcpy(g_store_path + g_store_path_len, store, store_len);
   g_store_path[g_store_path_len + store_len] = '\0';
 
-  FILE *fp = fopen(g_store_path, "rb");
-  if (fp == NULL) {
+  FILE *file = fopen(g_store_path, "rb");
+  if (file == NULL) {
     return -EINVAL;
   }
+  *fp = file;
+  return 0;
+}
+
+long
+oc_storage_size(const char *store)
+{
+  FILE *fp = NULL;
+  int ret = storage_open(store, &fp);
+  if (ret != 0) {
+    return ret;
+  }
+
+  if (fseek(fp, 0, SEEK_END) != 0) {
+    fclose(fp);
+    return -errno;
+  }
+  long fsize = ftell(fp);
+  if (fsize < 0) {
+    fclose(fp);
+    return -errno;
+  }
+  fclose(fp);
+  return fsize;
+}
+
+long
+oc_storage_read(const char *store, uint8_t *buf, size_t size)
+{
+  FILE *fp = NULL;
+  int ret = storage_open(store, &fp);
+  if (ret != 0) {
+    return ret;
+  }
 
   if (fseek(fp, 0, SEEK_END) != 0) {
     goto error;
diff --git a/port/arduino/adapter/storage.c b/port/arduino/adapter/storage.c
index 6e90ec6c71..8dc8602606 100644
--- a/port/arduino/adapter/storage.c
+++ b/port/arduino/adapter/storage.c
@@ -104,6 +104,12 @@ oc_storage_write(const char *store, const uint8_t *buf, size_t len)
   return len;
 }
 
+long
+oc_storage_size(const char *store)
+{
+  return -1;
+}
+
 long
 oc_storage_read(const char *store, uint8_t *buf, size_t len)
 {
diff --git a/port/esp32/adapter/src/storage.c b/port/esp32/adapter/src/storage.c
index 40aa9779d2..bc3cd5db57 100644
--- a/port/esp32/adapter/src/storage.c
+++ b/port/esp32/adapter/src/storage.c
@@ -92,31 +92,61 @@ oc_storage_reset(void)
   return 0;
 }
 
-long
-oc_storage_read(const char *store, uint8_t *buf, size_t size)
+static int
+storage_open(const char *store, nvs_handle_t *handle)
 {
-  OC_DBG("oc_storage_read: %s", store);
   if (!g_path_set) {
     return -ENOENT;
   }
-  nvs_handle_t handle;
+
   esp_err_t err =
-    nvs_open_from_partition(NVS_PARTITION, g_store_path, NVS_READONLY, &handle);
+    nvs_open_from_partition(NVS_PARTITION, g_store_path, NVS_READWRITE, handle);
   if (err != ESP_OK) {
     OC_ERR("oc_storage_read cannot nvs_open_from_partition %s: %s", store,
            esp_err_to_name(err));
     return -EINVAL;
   }
+  return 0;
+}
+
+long
+oc_storage_size(const char *store)
+{
+  nvs_handle_t handle;
+  int ret = storage_open(store, &handle);
+  if (ret < 0) {
+    return ret;
+  }
 
-  err = nvs_get_blob(handle, store, buf, &size);
+  size_t required_size;
+  esp_err_t err = nvs_get_blob(handle, store, NULL, &required_size);
   if (err != ESP_OK) {
     OC_ERR("oc_storage_read cannot nvs_get_blob  %s: %s", store,
            esp_err_to_name(err));
     nvs_close(handle);
     return -EINVAL;
   }
-  // TODO: check for overflow of buffer
+  nvs_close(handle);
+  return (long)required_size;
+}
 
+long
+oc_storage_read(const char *store, uint8_t *buf, size_t size)
+{
+  OC_DBG("oc_storage_read: %s", store);
+  nvs_handle_t handle;
+  int ret = storage_open(store, &handle);
+  if (ret < 0) {
+    return ret;
+  }
+
+  esp_err_t err = nvs_get_blob(handle, store, buf, &size);
+  if (err != ESP_OK) {
+    OC_ERR("oc_storage_read cannot nvs_get_blob  %s: %s", store,
+           esp_err_to_name(err));
+    nvs_close(handle);
+    return -EINVAL;
+  }
   nvs_close(handle);
   return size;
 }
diff --git a/port/linux/storage.c b/port/linux/storage.c
index 42a3bbbe5f..80f45fc4b2 100644
--- a/port/linux/storage.c
+++ b/port/linux/storage.c
@@ -100,18 +100,18 @@ oc_storage_reset(void)
   return 0;
 }
 
-long
-oc_storage_read(const char *store, uint8_t *buf, size_t size)
+static int
+storage_open(const char *store, FILE **fp)
 {
   if (g_store_path_len == 0) {
-    OC_ERR("failed to read from storage: store path is empty");
+    OC_ERR("failed to open storage: store path is empty");
     return -ENOENT;
   }
 
   size_t store_len = oc_strnlen_s(store, OC_STORE_PATH_SIZE);
   if ((store_len == 0) ||
       (store_len + g_store_path_len >= OC_STORE_PATH_SIZE)) {
-    OC_ERR("failed to read from storage: %s",
+    OC_ERR("failed to open storage: %s",
            store_len == 0
              ? "store path is empty"
              : "store path length is greater than " OC_EXPAND_TO_STR(
@@ -121,8 +121,8 @@ oc_storage_read(const char *store, uint8_t *buf, size_t size)
   memcpy(g_store_path + g_store_path_len, store, store_len);
   g_store_path[g_store_path_len + store_len] = '\0';
 
-  FILE *fp = fopen(g_store_path, "rb");
-  if (fp == NULL) {
+  FILE *file = fopen(g_store_path, "rb");
+  if (file == NULL) {
 #if OC_ERR_IS_ENABLED
     if (errno != ENOENT) {
       OC_ERR("failed to open %s for read: %d", g_store_path, errno);
@@ -133,6 +133,41 @@ oc_storage_read(const char *store, uint8_t *buf, size_t size)
     return -errno;
   }
 
+  *fp = file;
+  return 0;
+}
+
+long
+oc_storage_size(const char *store)
+{
+  FILE *fp = NULL;
+  int ret = storage_open(store, &fp);
+  if (ret != 0) {
+    return ret;
+  }
+
+  if (fseek(fp, 0, SEEK_END) != 0) {
+    fclose(fp);
+    return -errno;
+  }
+  long fsize = ftell(fp);
+  if (fsize < 0) {
+    fclose(fp);
+    return -errno;
+  }
+  fclose(fp);
+  return fsize;
+}
+
+long
+oc_storage_read(const char *store, uint8_t *buf, size_t size)
+{
+  FILE *fp = NULL;
+  int ret = storage_open(store, &fp);
+  if (ret < 0) {
+    return ret;
+  }
+
   if (fseek(fp, 0, SEEK_END) != 0) {
     OC_ERR("failed to fseek to the end of file %s: %d", g_store_path, errno);
     goto error;
diff --git a/port/oc_storage_internal.h b/port/oc_storage_internal.h
index 9e705678e7..a50ffa530f 100644
--- a/port/oc_storage_internal.h
+++ b/port/oc_storage_internal.h
@@ -19,6 +19,8 @@
 #ifndef OC_PORT_STORAGE_INTERNAL_H
 #define OC_PORT_STORAGE_INTERNAL_H
 
+#include "util/oc_compiler.h"
+
 #include <stdbool.h>
 #include <stddef.h>
 
@@ -44,6 +46,15 @@ int oc_storage_reset(void);
  */
 bool oc_storage_path(char *buffer, size_t buffer_size);
 
+/**
+ * @brief get size (in bytes) of the data written to store
+ *
+ * @param store the path to be read (cannot be NULL)
+ * @return <0 on failure
+ * @return >=0 size of the store
+ */
+long oc_storage_size(const char *store) OC_NONNULL();
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/port/unittest/storagetest.cpp b/port/unittest/storagetest.cpp
index 686a70f876..fc6adda893 100644
--- a/port/unittest/storagetest.cpp
+++ b/port/unittest/storagetest.cpp
@@ -55,19 +55,19 @@ class TestStorage : public testing::Test {
   void TearDown() override { ASSERT_EQ(0, oc_storage_reset()); }
 };
 
-TEST_F(TestStorage, oc_storage_config_fail)
+TEST_F(TestStorage, Config_Fail)
 {
   EXPECT_NE(0, oc_storage_config(nullptr));
   EXPECT_NE(0, oc_storage_config(""));
 }
 
-TEST_F(TestStorage, oc_storage_config_fail_append_slash)
+TEST_F(TestStorage, Config_FailAppendSlash)
 {
   auto path = std::string(OC_STORE_PATH_SIZE - 1, 'a');
   EXPECT_NE(0, oc_storage_config(path.c_str()));
 }
 
-TEST_F(TestStorage, oc_storage_config_fail_with_length_over)
+TEST_F(TestStorage, Config_FailWithLengthOver)
 {
   EXPECT_NE(
     0, oc_storage_config("./"
@@ -77,7 +77,7 @@ TEST_F(TestStorage, oc_storage_config_fail_with_length_over)
   EXPECT_FALSE(oc_storage_path(nullptr, 0));
 }
 
-TEST_F(TestStorage, oc_storage_config)
+TEST_F(TestStorage, Config)
 {
   EXPECT_EQ(0, oc_storage_config(testStorage.c_str()));
 
@@ -90,7 +90,7 @@ TEST_F(TestStorage, oc_storage_config)
   EXPECT_FALSE(oc_storage_path(nullptr, 0));
 }
 
-TEST_F(TestStorage, oc_storage_config_strip_trailing_slashes)
+TEST_F(TestStorage, Config_StripTrailingSlashes)
 {
   EXPECT_EQ(0, oc_storage_config(
                  (testStorage + std::string(5, kPathSeparator)).c_str()));
@@ -103,7 +103,7 @@ TEST_F(TestStorage, oc_storage_config_strip_trailing_slashes)
   EXPECT_FALSE(oc_storage_path(nullptr, 0));
 }
 
-TEST_F(TestStorage, oc_storage_path_fail)
+TEST_F(TestStorage, Path_Fail)
 {
   ASSERT_EQ(0, oc_storage_config(testStorage.c_str()));
 
@@ -111,7 +111,12 @@ TEST_F(TestStorage, oc_storage_path_fail)
   EXPECT_FALSE(oc_storage_path(too_small.data(), too_small.size()));
 }
 
-TEST_F(TestStorage, oc_storage_read_fail)
+TEST_F(TestStorage, Size)
+{
+  // TODO
+}
+
+TEST_F(TestStorage, Read_Fail)
 {
   // not configured
   std::array<uint8_t, 100> buf{};
@@ -126,7 +131,7 @@ TEST_F(TestStorage, oc_storage_read_fail)
   EXPECT_NE(0, oc_storage_read(store.c_str(), buf.data(), buf.size()));
 }
 
-TEST_F(TestStorage, oc_storage_write_fail)
+TEST_F(TestStorage, Write_Fail)
 {
   // not configured
   std::array<uint8_t, 100> buf{};
@@ -141,7 +146,7 @@ TEST_F(TestStorage, oc_storage_write_fail)
   EXPECT_NE(0, oc_storage_write(store.c_str(), buf.data(), buf.size()));
 }
 
-TEST_F(TestStorage, oc_storage_write)
+TEST_F(TestStorage, Write)
 {
   EXPECT_EQ(0, oc_storage_config(testStorage.c_str()));
 
diff --git a/port/windows/storage.c b/port/windows/storage.c
index 40e7a82562..837dcc79c7 100644
--- a/port/windows/storage.c
+++ b/port/windows/storage.c
@@ -92,8 +92,8 @@ oc_storage_reset(void)
   return 0;
 }
 
-long
-oc_storage_read(const char *store, uint8_t *buf, size_t size)
+static int
+storage_open(const char *store, FILE **fp)
 {
   if (g_store_path_len == 0) {
     return -ENOENT;
@@ -107,10 +107,44 @@ oc_storage_read(const char *store, uint8_t *buf, size_t size)
   memcpy(g_store_path + g_store_path_len, store, store_len);
   g_store_path[g_store_path_len + store_len] = '\0';
 
-  FILE *fp = fopen(g_store_path, "rb");
-  if (fp == NULL) {
+  FILE *file = fopen(g_store_path, "rb");
+  if (file == NULL) {
     return -EINVAL;
   }
+  *fp = file;
+  return 0;
+}
+
+long
+oc_storage_size(const char *store)
+{
+  FILE *fp = NULL;
+  int ret = storage_open(store, &fp);
+  if (ret != 0) {
+    return ret;
+  }
+
+  if (fseek(fp, 0, SEEK_END) != 0) {
+    fclose(fp);
+    return -errno;
+  }
+  long fsize = ftell(fp);
+  if (fsize < 0) {
+    fclose(fp);
+    return -errno;
+  }
+  fclose(fp);
+  return fsize;
+}
+
+long
+oc_storage_read(const char *store, uint8_t *buf, size_t size)
+{
+  FILE *fp = NULL;
+  int ret = storage_open(store, &fp);
+  if (ret != 0) {
+    return ret;
+  }
 
   if (fseek(fp, 0, SEEK_END) != 0) {
     goto error;
diff --git a/port/zephyr/src/storage.c b/port/zephyr/src/storage.c
index 297a93033f..4cd6f7136a 100644
--- a/port/zephyr/src/storage.c
+++ b/port/zephyr/src/storage.c
@@ -290,6 +290,12 @@ find_key(const char *store)
   return NULL;
 }
 
+long
+oc_storage_size(const char *store)
+{
+  return -1;
+}
+
 /*
  * store should contains the memory position to read.
  * The value should be multiple of the flash sector size.