diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4e727bb791..54051db0d2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@ Please mark all change in change log and use the issue from GitHub
 ## Bug
 -   \#1762 Server is not forbidden to create new partition which tag is `_default`
 -   \#1873 Fix index file serialize to incorrect path
+-   \#1881 Fix Annoy index search fail
 
 ## Feature
 -   \#261  Integrate ANNOY into Milvus
diff --git a/core/src/codecs/default/DefaultVectorIndexFormat.cpp b/core/src/codecs/default/DefaultVectorIndexFormat.cpp
index 4ce2b2f4cd..71df5ea73a 100644
--- a/core/src/codecs/default/DefaultVectorIndexFormat.cpp
+++ b/core/src/codecs/default/DefaultVectorIndexFormat.cpp
@@ -36,9 +36,12 @@ DefaultVectorIndexFormat::read_internal(const storage::FSHandlerPtr& fs_ptr, con
     knowhere::BinarySet load_data_list;
 
     recorder.RecordSection("Start");
-    fs_ptr->reader_ptr_->open(path);
+    if (!fs_ptr->reader_ptr_->open(path)) {
+        ENGINE_LOG_ERROR << "Fail to open vector index: " << path;
+        return nullptr;
+    }
 
-    size_t length = fs_ptr->reader_ptr_->length();
+    int64_t length = fs_ptr->reader_ptr_->length();
     if (length <= 0) {
         ENGINE_LOG_ERROR << "Invalid vector index length: " << path;
         return nullptr;
@@ -128,7 +131,10 @@ DefaultVectorIndexFormat::write(const storage::FSHandlerPtr& fs_ptr, const std::
     int32_t index_type = knowhere::StrToOldIndexType(index->index_type());
 
     recorder.RecordSection("Start");
-    fs_ptr->writer_ptr_->open(location);
+    if (!fs_ptr->writer_ptr_->open(location)) {
+        ENGINE_LOG_ERROR << "Fail to open vector index: " << location;
+        return;
+    }
 
     fs_ptr->writer_ptr_->write(&index_type, sizeof(index_type));
 
diff --git a/core/src/storage/IOReader.h b/core/src/storage/IOReader.h
index eeddb7438b..98fabcefc4 100644
--- a/core/src/storage/IOReader.h
+++ b/core/src/storage/IOReader.h
@@ -19,16 +19,16 @@ namespace storage {
 
 class IOReader {
  public:
-    virtual void
+    virtual bool
     open(const std::string& name) = 0;
 
     virtual void
-    read(void* ptr, size_t size) = 0;
+    read(void* ptr, int64_t size) = 0;
 
     virtual void
-    seekg(size_t pos) = 0;
+    seekg(int64_t pos) = 0;
 
-    virtual size_t
+    virtual int64_t
     length() = 0;
 
     virtual void
diff --git a/core/src/storage/IOWriter.h b/core/src/storage/IOWriter.h
index 38b6887057..763174b11c 100644
--- a/core/src/storage/IOWriter.h
+++ b/core/src/storage/IOWriter.h
@@ -19,13 +19,13 @@ namespace storage {
 
 class IOWriter {
  public:
-    virtual void
+    virtual bool
     open(const std::string& name) = 0;
 
     virtual void
-    write(void* ptr, size_t size) = 0;
+    write(void* ptr, int64_t size) = 0;
 
-    virtual size_t
+    virtual int64_t
     length() = 0;
 
     virtual void
diff --git a/core/src/storage/disk/DiskIOReader.cpp b/core/src/storage/disk/DiskIOReader.cpp
index f51ffef0b3..ba5aa30dd3 100644
--- a/core/src/storage/disk/DiskIOReader.cpp
+++ b/core/src/storage/disk/DiskIOReader.cpp
@@ -14,26 +14,27 @@
 namespace milvus {
 namespace storage {
 
-void
+bool
 DiskIOReader::open(const std::string& name) {
     name_ = name;
     fs_ = std::fstream(name_, std::ios::in | std::ios::binary);
+    return fs_.good();
 }
 
 void
-DiskIOReader::read(void* ptr, size_t size) {
+DiskIOReader::read(void* ptr, int64_t size) {
     fs_.read(reinterpret_cast<char*>(ptr), size);
 }
 
 void
-DiskIOReader::seekg(size_t pos) {
+DiskIOReader::seekg(int64_t pos) {
     fs_.seekg(pos);
 }
 
-size_t
+int64_t
 DiskIOReader::length() {
     fs_.seekg(0, fs_.end);
-    size_t len = fs_.tellg();
+    int64_t len = fs_.tellg();
     fs_.seekg(0, fs_.beg);
     return len;
 }
diff --git a/core/src/storage/disk/DiskIOReader.h b/core/src/storage/disk/DiskIOReader.h
index 09d2e27955..363564c5a9 100644
--- a/core/src/storage/disk/DiskIOReader.h
+++ b/core/src/storage/disk/DiskIOReader.h
@@ -33,16 +33,16 @@ class DiskIOReader : public IOReader {
     DiskIOReader&
     operator=(DiskIOReader&&) = delete;
 
-    void
+    bool
     open(const std::string& name) override;
 
     void
-    read(void* ptr, size_t size) override;
+    read(void* ptr, int64_t size) override;
 
     void
-    seekg(size_t pos) override;
+    seekg(int64_t pos) override;
 
-    size_t
+    int64_t
     length() override;
 
     void
diff --git a/core/src/storage/disk/DiskIOWriter.cpp b/core/src/storage/disk/DiskIOWriter.cpp
index 63899463b1..75bc84e82e 100644
--- a/core/src/storage/disk/DiskIOWriter.cpp
+++ b/core/src/storage/disk/DiskIOWriter.cpp
@@ -14,20 +14,21 @@
 namespace milvus {
 namespace storage {
 
-void
+bool
 DiskIOWriter::open(const std::string& name) {
     name_ = name;
     len_ = 0;
     fs_ = std::fstream(name_, std::ios::out | std::ios::binary);
+    return fs_.good();
 }
 
 void
-DiskIOWriter::write(void* ptr, size_t size) {
+DiskIOWriter::write(void* ptr, int64_t size) {
     fs_.write(reinterpret_cast<char*>(ptr), size);
     len_ += size;
 }
 
-size_t
+int64_t
 DiskIOWriter::length() {
     return len_;
 }
diff --git a/core/src/storage/disk/DiskIOWriter.h b/core/src/storage/disk/DiskIOWriter.h
index d803c9dd39..051c9fb5fe 100644
--- a/core/src/storage/disk/DiskIOWriter.h
+++ b/core/src/storage/disk/DiskIOWriter.h
@@ -33,13 +33,13 @@ class DiskIOWriter : public IOWriter {
     DiskIOWriter&
     operator=(DiskIOWriter&&) = delete;
 
-    void
+    bool
     open(const std::string& name) override;
 
     void
-    write(void* ptr, size_t size) override;
+    write(void* ptr, int64_t size) override;
 
-    size_t
+    int64_t
     length() override;
 
     void
@@ -47,7 +47,7 @@ class DiskIOWriter : public IOWriter {
 
  public:
     std::string name_;
-    size_t len_;
+    int64_t len_;
     std::fstream fs_;
 };
 
diff --git a/core/src/storage/s3/S3IOReader.cpp b/core/src/storage/s3/S3IOReader.cpp
index e8d073029a..a2b33ef3f9 100644
--- a/core/src/storage/s3/S3IOReader.cpp
+++ b/core/src/storage/s3/S3IOReader.cpp
@@ -15,24 +15,24 @@
 namespace milvus {
 namespace storage {
 
-void
+bool
 S3IOReader::open(const std::string& name) {
     name_ = name;
     pos_ = 0;
-    S3ClientWrapper::GetInstance().GetObjectStr(name_, buffer_);
+    return (S3ClientWrapper::GetInstance().GetObjectStr(name_, buffer_).ok());
 }
 
 void
-S3IOReader::read(void* ptr, size_t size) {
+S3IOReader::read(void* ptr, int64_t size) {
     memcpy(ptr, buffer_.data() + pos_, size);
 }
 
 void
-S3IOReader::seekg(size_t pos) {
+S3IOReader::seekg(int64_t pos) {
     pos_ = pos;
 }
 
-size_t
+int64_t
 S3IOReader::length() {
     return buffer_.length();
 }
diff --git a/core/src/storage/s3/S3IOReader.h b/core/src/storage/s3/S3IOReader.h
index 3311ff1297..623a3ff878 100644
--- a/core/src/storage/s3/S3IOReader.h
+++ b/core/src/storage/s3/S3IOReader.h
@@ -32,16 +32,16 @@ class S3IOReader : public IOReader {
     S3IOReader&
     operator=(S3IOReader&&) = delete;
 
-    void
+    bool
     open(const std::string& name) override;
 
     void
-    read(void* ptr, size_t size) override;
+    read(void* ptr, int64_t size) override;
 
     void
-    seekg(size_t pos) override;
+    seekg(int64_t pos) override;
 
-    size_t
+    int64_t
     length() override;
 
     void
@@ -50,7 +50,7 @@ class S3IOReader : public IOReader {
  public:
     std::string name_;
     std::string buffer_;
-    size_t pos_;
+    int64_t pos_;
 };
 
 using S3IOReaderPtr = std::shared_ptr<S3IOReader>;
diff --git a/core/src/storage/s3/S3IOWriter.cpp b/core/src/storage/s3/S3IOWriter.cpp
index 9d00db3c83..68acb374a3 100644
--- a/core/src/storage/s3/S3IOWriter.cpp
+++ b/core/src/storage/s3/S3IOWriter.cpp
@@ -15,20 +15,21 @@
 namespace milvus {
 namespace storage {
 
-void
+bool
 S3IOWriter::open(const std::string& name) {
     name_ = name;
     len_ = 0;
     buffer_ = "";
+    return true;
 }
 
 void
-S3IOWriter::write(void* ptr, size_t size) {
+S3IOWriter::write(void* ptr, int64_t size) {
     buffer_ += std::string(reinterpret_cast<char*>(ptr), size);
     len_ += size;
 }
 
-size_t
+int64_t
 S3IOWriter::length() {
     return len_;
 }
diff --git a/core/src/storage/s3/S3IOWriter.h b/core/src/storage/s3/S3IOWriter.h
index 712e74b722..ba1b3510ae 100644
--- a/core/src/storage/s3/S3IOWriter.h
+++ b/core/src/storage/s3/S3IOWriter.h
@@ -32,13 +32,13 @@ class S3IOWriter : public IOWriter {
     S3IOWriter&
     operator=(S3IOWriter&&) = delete;
 
-    void
+    bool
     open(const std::string& name) override;
 
     void
-    write(void* ptr, size_t size) override;
+    write(void* ptr, int64_t size) override;
 
-    size_t
+    int64_t
     length() override;
 
     void
@@ -46,7 +46,7 @@ class S3IOWriter : public IOWriter {
 
  public:
     std::string name_;
-    size_t len_;
+    int64_t len_;
     std::string buffer_;
 };
 
diff --git a/core/unittest/CMakeLists.txt b/core/unittest/CMakeLists.txt
index 85855a11df..0c57df086a 100644
--- a/core/unittest/CMakeLists.txt
+++ b/core/unittest/CMakeLists.txt
@@ -208,4 +208,4 @@ add_subdirectory(metrics)
 add_subdirectory(scheduler)
 add_subdirectory(server)
 add_subdirectory(thirdparty)
-#add_subdirectory(storage)
+add_subdirectory(storage)
diff --git a/core/unittest/storage/CMakeLists.txt b/core/unittest/storage/CMakeLists.txt
index 75df76f197..5294935af0 100644
--- a/core/unittest/storage/CMakeLists.txt
+++ b/core/unittest/storage/CMakeLists.txt
@@ -12,7 +12,8 @@
 #-------------------------------------------------------------------------------
 
 set(test_files
-        ${CMAKE_CURRENT_SOURCE_DIR}/test_s3_client.cpp
+#        ${CMAKE_CURRENT_SOURCE_DIR}/test_s3_client.cpp
+        ${CMAKE_CURRENT_SOURCE_DIR}/test_disk.cpp
         ${CMAKE_CURRENT_SOURCE_DIR}/utils.cpp
         )
 
diff --git a/core/unittest/storage/test_disk.cpp b/core/unittest/storage/test_disk.cpp
new file mode 100644
index 0000000000..ef43594687
--- /dev/null
+++ b/core/unittest/storage/test_disk.cpp
@@ -0,0 +1,62 @@
+// Copyright (C) 2019-2020 Zilliz. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software distributed under the License
+// is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+// or implied. See the License for the specific language governing permissions and limitations under the License.
+
+#include <gtest/gtest.h>
+
+#include "easyloggingpp/easylogging++.h"
+#include "storage/disk/DiskIOReader.h"
+#include "storage/disk/DiskIOWriter.h"
+#include "storage/utils.h"
+
+INITIALIZE_EASYLOGGINGPP
+
+TEST_F(StorageTest, DISK_RW_TEST) {
+    const std::string index_name = "/tmp/test_index";
+    const std::string content = "abcdefg";
+
+    {
+        milvus::storage::DiskIOWriter writer;
+        ASSERT_TRUE(writer.open(index_name));
+        size_t len = content.length();
+        writer.write(&len, sizeof(len));
+        writer.write((void*)(content.data()), len);
+        ASSERT_TRUE(len + sizeof(len) == writer.length());
+        writer.close();
+    }
+
+    {
+        milvus::storage::DiskIOReader reader;
+        ASSERT_FALSE(reader.open("/tmp/notexist"));
+        ASSERT_TRUE(reader.open(index_name));
+        int64_t length = reader.length();
+        int64_t rp = 0;
+        reader.seekg(rp);
+        std::string content_out;
+        while (rp < length) {
+            size_t len;
+            reader.read(&len, sizeof(len));
+            rp += sizeof(len);
+            reader.seekg(rp);
+
+            auto data = new char[len];
+            reader.read(data, len);
+            rp += len;
+            reader.seekg(rp);
+
+            content_out += std::string(data, len);
+
+            delete[] data;
+        }
+
+        ASSERT_TRUE(content == content_out);
+        reader.close();
+    }
+}