diff --git a/CMakeLists.txt b/CMakeLists.txt
index 51749bae0..3a0068eef 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -244,6 +244,7 @@ set(SOURCES
         utilities/document/document_db.cc
         utilities/document/json_document.cc
         utilities/document/json_document_builder.cc
+	utilities/env_mirror.cc
         utilities/flashcache/flashcache.cc
         utilities/geodb/geodb_impl.cc
         utilities/leveldb_options/leveldb_options.cc
diff --git a/Makefile b/Makefile
index 2ef49fb3c..5ba47fc26 100644
--- a/Makefile
+++ b/Makefile
@@ -805,6 +805,9 @@ json_document_test: utilities/document/json_document_test.o $(LIBOBJECTS) $(TEST
 spatial_db_test: utilities/spatialdb/spatial_db_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
 
+env_mirror_test: utilities/env_mirror_test.o $(LIBOBJECTS) $(TESTHARNESS)
+	$(AM_LINK)
+
 ttl_test: utilities/ttl/ttl_test.o $(LIBOBJECTS) $(TESTHARNESS)
 	$(AM_LINK)
 
diff --git a/include/rocksdb/env.h b/include/rocksdb/env.h
index 00fa52001..ebaeee6cc 100644
--- a/include/rocksdb/env.h
+++ b/include/rocksdb/env.h
@@ -615,6 +615,7 @@ class WritableFile {
 
  protected:
   friend class WritableFileWrapper;
+  friend class WritableFileMirror;
 
   Env::IOPriority io_priority_;
 };
diff --git a/include/rocksdb/utilities/env_mirror.h b/include/rocksdb/utilities/env_mirror.h
new file mode 100644
index 000000000..021fbfa45
--- /dev/null
+++ b/include/rocksdb/utilities/env_mirror.h
@@ -0,0 +1,166 @@
+// Copyright (c) 2015, Red Hat, Inc.  All rights reserved.
+// This source code is licensed under the BSD-style license found in the
+// LICENSE file in the root directory of this source tree. An additional grant
+// of patent rights can be found in the PATENTS file in the same directory.
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+//
+// MirrorEnv is an Env implementation that mirrors all file-related
+// operations to two backing Env's (provided at construction time).
+// Writes are mirrored.  For read operations, we do the read from both
+// backends and assert that the results match.
+//
+// This is useful when implementing a new Env and ensuring that the
+// semantics and behavior are correct (in that they match that of an
+// existing, stable Env, like the default POSIX one).
+
+#ifndef ROCKSDB_LITE
+
+#ifndef STORAGE_ROCKSDB_INCLUDE_UTILITIES_ENVMIRROR_H_
+#define STORAGE_ROCKSDB_INCLUDE_UTLIITIES_ENVMIRROR_H_
+
+#include <iostream>
+#include <algorithm>
+#include <vector>
+#include "rocksdb/env.h"
+
+namespace rocksdb {
+
+class SequentialFileMirror;
+class RandomAccessFileMirror;
+class WritableFileMirror;
+
+class EnvMirror : public EnvWrapper {
+  Env* a_, *b_;
+
+ public:
+  EnvMirror(Env* a, Env* b) : EnvWrapper(a), a_(a), b_(b) {}
+
+  Status NewSequentialFile(const std::string& f, unique_ptr<SequentialFile>* r,
+                           const EnvOptions& options) override;
+  Status NewRandomAccessFile(const std::string& f,
+                             unique_ptr<RandomAccessFile>* r,
+                             const EnvOptions& options) override;
+  Status NewWritableFile(const std::string& f, unique_ptr<WritableFile>* r,
+                         const EnvOptions& options) override;
+  Status ReuseWritableFile(const std::string& fname,
+                           const std::string& old_fname,
+                           unique_ptr<WritableFile>* r,
+                           const EnvOptions& options) override;
+  virtual Status NewDirectory(const std::string& name,
+                              unique_ptr<Directory>* result) override {
+    unique_ptr<Directory> br;
+    Status as = a_->NewDirectory(name, result);
+    Status bs = b_->NewDirectory(name, &br);
+    assert(as == bs);
+    return as;
+  }
+  Status FileExists(const std::string& f) override {
+    Status as = a_->FileExists(f);
+    Status bs = b_->FileExists(f);
+    assert(as == bs);
+    return as;
+  }
+  Status GetChildren(const std::string& dir,
+                     std::vector<std::string>* r) override {
+    std::vector<std::string> ar, br;
+    Status as = a_->GetChildren(dir, &ar);
+    Status bs = b_->GetChildren(dir, &br);
+    assert(as == bs);
+    std::sort(ar.begin(), ar.end());
+    std::sort(br.begin(), br.end());
+    if (!as.ok() || ar != br) {
+      assert(0 == "getchildren results don't match");
+    }
+    *r = ar;
+    return as;
+  }
+  Status DeleteFile(const std::string& f) override {
+    Status as = a_->DeleteFile(f);
+    Status bs = b_->DeleteFile(f);
+    assert(as == bs);
+    return as;
+  }
+  Status CreateDir(const std::string& d) override {
+    Status as = a_->CreateDir(d);
+    Status bs = b_->CreateDir(d);
+    assert(as == bs);
+    return as;
+  }
+  Status CreateDirIfMissing(const std::string& d) override {
+    Status as = a_->CreateDirIfMissing(d);
+    Status bs = b_->CreateDirIfMissing(d);
+    assert(as == bs);
+    return as;
+  }
+  Status DeleteDir(const std::string& d) override {
+    Status as = a_->DeleteDir(d);
+    Status bs = b_->DeleteDir(d);
+    assert(as == bs);
+    return as;
+  }
+  Status GetFileSize(const std::string& f, uint64_t* s) override {
+    uint64_t asize, bsize;
+    Status as = a_->GetFileSize(f, &asize);
+    Status bs = b_->GetFileSize(f, &bsize);
+    assert(as == bs);
+    assert(!as.ok() || asize == bsize);
+    *s = asize;
+    return as;
+  }
+
+  Status GetFileModificationTime(const std::string& fname,
+                                 uint64_t* file_mtime) override {
+    uint64_t amtime, bmtime;
+    Status as = a_->GetFileModificationTime(fname, &amtime);
+    Status bs = b_->GetFileModificationTime(fname, &bmtime);
+    assert(as == bs);
+    assert(!as.ok() || amtime - bmtime < 10000 || bmtime - amtime < 10000);
+    *file_mtime = amtime;
+    return as;
+  }
+
+  Status RenameFile(const std::string& s, const std::string& t) override {
+    Status as = a_->RenameFile(s, t);
+    Status bs = b_->RenameFile(s, t);
+    assert(as == bs);
+    return as;
+  }
+
+  Status LinkFile(const std::string& s, const std::string& t) override {
+    Status as = a_->LinkFile(s, t);
+    Status bs = b_->LinkFile(s, t);
+    assert(as == bs);
+    return as;
+  }
+
+  class FileLockMirror : public FileLock {
+   public:
+    FileLock* a_, *b_;
+    FileLockMirror(FileLock* a, FileLock* b) : a_(a), b_(b) {}
+  };
+
+  Status LockFile(const std::string& f, FileLock** l) override {
+    FileLock* al, *bl;
+    Status as = a_->LockFile(f, &al);
+    Status bs = b_->LockFile(f, &bl);
+    assert(as == bs);
+    if (as.ok()) *l = new FileLockMirror(al, bl);
+    return as;
+  }
+
+  Status UnlockFile(FileLock* l) override {
+    FileLockMirror* ml = static_cast<FileLockMirror*>(l);
+    Status as = a_->UnlockFile(ml->a_);
+    Status bs = b_->UnlockFile(ml->b_);
+    assert(as == bs);
+    return as;
+  }
+};
+
+}  // namespace rocksdb
+
+#endif  // STORAGE_ROCKSDB_INCLUDE_UTILITIES_ENVMIRROR_H_
+
+#endif  // ROCKSDB_LITE
diff --git a/src.mk b/src.mk
index 05c084ac5..9834d30d9 100644
--- a/src.mk
+++ b/src.mk
@@ -110,6 +110,7 @@ LIB_SOURCES =                                                   \
   utilities/document/document_db.cc                             \
   utilities/document/json_document_builder.cc                   \
   utilities/document/json_document.cc                           \
+  utilities/env_mirror.cc                                       \
   utilities/flashcache/flashcache.cc                            \
   utilities/geodb/geodb_impl.cc                                 \
   utilities/leveldb_options/leveldb_options.cc                  \
diff --git a/utilities/env_mirror.cc b/utilities/env_mirror.cc
new file mode 100644
index 000000000..806711382
--- /dev/null
+++ b/utilities/env_mirror.cc
@@ -0,0 +1,266 @@
+// Copyright (c) 2015, Red Hat, Inc.  All rights reserved.
+// This source code is licensed under the BSD-style license found in the
+// LICENSE file in the root directory of this source tree. An additional grant
+// of patent rights can be found in the PATENTS file in the same directory.
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+#ifndef ROCKSDB_LITE
+
+#include "rocksdb/utilities/env_mirror.h"
+
+namespace rocksdb {
+
+// An implementaiton of Env that mirrors all work over two backend
+// Env's.  This is useful for debugging purposes.
+class SequentialFileMirror : public SequentialFile {
+ public:
+  unique_ptr<SequentialFile> a_, b_;
+  std::string fname;
+  SequentialFileMirror(std::string f) : fname(f) {}
+
+  Status Read(size_t n, Slice* result, char* scratch) {
+    Slice aslice;
+    Status as = a_->Read(n, &aslice, scratch);
+    if (as == Status::OK()) {
+      char* bscratch = new char[n];
+      Slice bslice;
+      size_t off = 0;
+      size_t left = aslice.size();
+      while (left) {
+        Status bs = b_->Read(left, &bslice, bscratch);
+        assert(as == bs);
+        assert(memcmp(bscratch, scratch + off, bslice.size()) == 0);
+        off += bslice.size();
+        left -= bslice.size();
+      }
+      delete[] bscratch;
+      *result = aslice;
+    } else {
+      Status bs = b_->Read(n, result, scratch);
+      assert(as == bs);
+    }
+    return as;
+  }
+
+  Status Skip(uint64_t n) {
+    Status as = a_->Skip(n);
+    Status bs = b_->Skip(n);
+    assert(as == bs);
+    return as;
+  }
+  Status InvalidateCache(size_t offset, size_t length) {
+    Status as = a_->InvalidateCache(offset, length);
+    Status bs = b_->InvalidateCache(offset, length);
+    assert(as == bs);
+    return as;
+  };
+};
+
+class RandomAccessFileMirror : public RandomAccessFile {
+ public:
+  unique_ptr<RandomAccessFile> a_, b_;
+  std::string fname;
+  RandomAccessFileMirror(std::string f) : fname(f) {}
+
+  Status Read(uint64_t offset, size_t n, Slice* result, char* scratch) const {
+    Status as = a_->Read(offset, n, result, scratch);
+    if (as == Status::OK()) {
+      char* bscratch = new char[n];
+      Slice bslice;
+      size_t off = 0;
+      size_t left = result->size();
+      while (left) {
+        Status bs = b_->Read(offset + off, left, &bslice, bscratch);
+        assert(as == bs);
+        assert(memcmp(bscratch, scratch + off, bslice.size()) == 0);
+        off += bslice.size();
+        left -= bslice.size();
+      }
+      delete[] bscratch;
+    } else {
+      Status bs = b_->Read(offset, n, result, scratch);
+      assert(as == bs);
+    }
+    return as;
+  }
+
+  bool ShouldForwardRawRequest() const {
+    // NOTE: not verified
+    return a_->ShouldForwardRawRequest();
+  }
+
+  size_t GetUniqueId(char* id, size_t max_size) const {
+    // NOTE: not verified
+    return a_->GetUniqueId(id, max_size);
+  }
+};
+
+class WritableFileMirror : public WritableFile {
+ public:
+  unique_ptr<WritableFile> a_, b_;
+  std::string fname;
+  WritableFileMirror(std::string f) : fname(f) {}
+
+  Status Append(const Slice& data) override {
+    Status as = a_->Append(data);
+    Status bs = b_->Append(data);
+    assert(as == bs);
+    return as;
+  }
+  Status PositionedAppend(const Slice& data, uint64_t offset) override {
+    Status as = a_->PositionedAppend(data, offset);
+    Status bs = b_->PositionedAppend(data, offset);
+    assert(as == bs);
+    return as;
+  }
+  Status Truncate(uint64_t size) override {
+    Status as = a_->Truncate(size);
+    Status bs = b_->Truncate(size);
+    assert(as == bs);
+    return as;
+  }
+  Status Close() override {
+    Status as = a_->Close();
+    Status bs = b_->Close();
+    assert(as == bs);
+    return as;
+  }
+  Status Flush() override {
+    Status as = a_->Flush();
+    Status bs = b_->Flush();
+    assert(as == bs);
+    return as;
+  }
+  Status Sync() override {
+    Status as = a_->Sync();
+    Status bs = b_->Sync();
+    assert(as == bs);
+    return as;
+  }
+  Status Fsync() override {
+    Status as = a_->Fsync();
+    Status bs = b_->Fsync();
+    assert(as == bs);
+    return as;
+  }
+  bool IsSyncThreadSafe() const override {
+    bool as = a_->IsSyncThreadSafe();
+    bool bs = b_->IsSyncThreadSafe();
+    assert(as == bs);
+    return as;
+  }
+  void SetIOPriority(Env::IOPriority pri) override {
+    a_->SetIOPriority(pri);
+    b_->SetIOPriority(pri);
+  }
+  Env::IOPriority GetIOPriority() override {
+    // NOTE: we don't verify this one
+    return a_->GetIOPriority();
+  }
+  uint64_t GetFileSize() override {
+    uint64_t as = a_->GetFileSize();
+    uint64_t bs = b_->GetFileSize();
+    assert(as == bs);
+    return as;
+  }
+  void GetPreallocationStatus(size_t* block_size,
+                              size_t* last_allocated_block) override {
+    // NOTE: we don't verify this one
+    return a_->GetPreallocationStatus(block_size, last_allocated_block);
+  }
+  size_t GetUniqueId(char* id, size_t max_size) const override {
+    // NOTE: we don't verify this one
+    return a_->GetUniqueId(id, max_size);
+  }
+  Status InvalidateCache(size_t offset, size_t length) override {
+    Status as = a_->InvalidateCache(offset, length);
+    Status bs = b_->InvalidateCache(offset, length);
+    assert(as == bs);
+    return as;
+  }
+
+ protected:
+  Status Allocate(uint64_t offset, uint64_t length) override {
+    Status as = a_->Allocate(offset, length);
+    Status bs = b_->Allocate(offset, length);
+    assert(as == bs);
+    return as;
+  }
+  Status RangeSync(uint64_t offset, uint64_t nbytes) override {
+    Status as = a_->RangeSync(offset, nbytes);
+    Status bs = b_->RangeSync(offset, nbytes);
+    assert(as == bs);
+    return as;
+  }
+};
+
+Status EnvMirror::NewSequentialFile(const std::string& f,
+                                    unique_ptr<SequentialFile>* r,
+                                    const EnvOptions& options) {
+  if (f.find("/proc/") == 0) {
+    return a_->NewSequentialFile(f, r, options);
+  }
+  SequentialFileMirror* mf = new SequentialFileMirror(f);
+  Status as = a_->NewSequentialFile(f, &mf->a_, options);
+  Status bs = b_->NewSequentialFile(f, &mf->b_, options);
+  assert(as == bs);
+  if (as.ok())
+    r->reset(mf);
+  else
+    delete mf;
+  return as;
+}
+
+Status EnvMirror::NewRandomAccessFile(const std::string& f,
+                                      unique_ptr<RandomAccessFile>* r,
+                                      const EnvOptions& options) {
+  if (f.find("/proc/") == 0) {
+    return a_->NewRandomAccessFile(f, r, options);
+  }
+  RandomAccessFileMirror* mf = new RandomAccessFileMirror(f);
+  Status as = a_->NewRandomAccessFile(f, &mf->a_, options);
+  Status bs = b_->NewRandomAccessFile(f, &mf->b_, options);
+  assert(as == bs);
+  if (as.ok())
+    r->reset(mf);
+  else
+    delete mf;
+  return as;
+}
+
+Status EnvMirror::NewWritableFile(const std::string& f,
+                                  unique_ptr<WritableFile>* r,
+                                  const EnvOptions& options) {
+  if (f.find("/proc/") == 0) return a_->NewWritableFile(f, r, options);
+  WritableFileMirror* mf = new WritableFileMirror(f);
+  Status as = a_->NewWritableFile(f, &mf->a_, options);
+  Status bs = b_->NewWritableFile(f, &mf->b_, options);
+  assert(as == bs);
+  if (as.ok())
+    r->reset(mf);
+  else
+    delete mf;
+  return as;
+}
+
+Status EnvMirror::ReuseWritableFile(const std::string& fname,
+                                    const std::string& old_fname,
+                                    unique_ptr<WritableFile>* r,
+                                    const EnvOptions& options) {
+  if (fname.find("/proc/") == 0)
+    return a_->ReuseWritableFile(fname, old_fname, r, options);
+  WritableFileMirror* mf = new WritableFileMirror(fname);
+  Status as = a_->ReuseWritableFile(fname, old_fname, &mf->a_, options);
+  Status bs = b_->ReuseWritableFile(fname, old_fname, &mf->b_, options);
+  assert(as == bs);
+  if (as.ok())
+    r->reset(mf);
+  else
+    delete mf;
+  return as;
+}
+
+}  // namespace rocksdb
+#endif
diff --git a/utilities/env_mirror_test.cc b/utilities/env_mirror_test.cc
new file mode 100644
index 000000000..845356bf6
--- /dev/null
+++ b/utilities/env_mirror_test.cc
@@ -0,0 +1,222 @@
+//  Copyright (c) 2015, Red Hat, Inc.  All rights reserved.
+//  This source code is licensed under the BSD-style license found in the
+//  LICENSE file in the root directory of this source tree. An additional grant
+//  of patent rights can be found in the PATENTS file in the same directory.
+
+#ifndef ROCKSDB_LITE
+
+#include "rocksdb/utilities/env_mirror.h"
+#include "util/mock_env.h"
+#include "util/testharness.h"
+
+namespace rocksdb {
+
+class EnvMirrorTest : public testing::Test {
+ public:
+  Env* default_;
+  MockEnv* a_, *b_;
+  EnvMirror* env_;
+  const EnvOptions soptions_;
+
+  EnvMirrorTest()
+      : default_(Env::Default()),
+        a_(new MockEnv(default_)),
+        b_(new MockEnv(default_)),
+        env_(new EnvMirror(a_, b_)) {}
+  ~EnvMirrorTest() {
+    delete env_;
+    delete a_;
+    delete b_;
+  }
+};
+
+TEST_F(EnvMirrorTest, Basics) {
+  uint64_t file_size;
+  unique_ptr<WritableFile> writable_file;
+  std::vector<std::string> children;
+
+  ASSERT_OK(env_->CreateDir("/dir"));
+
+  // Check that the directory is empty.
+  ASSERT_EQ(Status::NotFound(), env_->FileExists("/dir/non_existent"));
+  ASSERT_TRUE(!env_->GetFileSize("/dir/non_existent", &file_size).ok());
+  ASSERT_OK(env_->GetChildren("/dir", &children));
+  ASSERT_EQ(0U, children.size());
+
+  // Create a file.
+  ASSERT_OK(env_->NewWritableFile("/dir/f", &writable_file, soptions_));
+  writable_file.reset();
+
+  // Check that the file exists.
+  ASSERT_OK(env_->FileExists("/dir/f"));
+  ASSERT_OK(a_->FileExists("/dir/f"));
+  ASSERT_OK(b_->FileExists("/dir/f"));
+  ASSERT_OK(env_->GetFileSize("/dir/f", &file_size));
+  ASSERT_EQ(0U, file_size);
+  ASSERT_OK(env_->GetChildren("/dir", &children));
+  ASSERT_EQ(1U, children.size());
+  ASSERT_EQ("f", children[0]);
+  ASSERT_OK(a_->GetChildren("/dir", &children));
+  ASSERT_EQ(1U, children.size());
+  ASSERT_EQ("f", children[0]);
+  ASSERT_OK(b_->GetChildren("/dir", &children));
+  ASSERT_EQ(1U, children.size());
+  ASSERT_EQ("f", children[0]);
+
+  // Write to the file.
+  ASSERT_OK(env_->NewWritableFile("/dir/f", &writable_file, soptions_));
+  ASSERT_OK(writable_file->Append("abc"));
+  writable_file.reset();
+
+  // Check for expected size.
+  ASSERT_OK(env_->GetFileSize("/dir/f", &file_size));
+  ASSERT_EQ(3U, file_size);
+  ASSERT_OK(a_->GetFileSize("/dir/f", &file_size));
+  ASSERT_EQ(3U, file_size);
+  ASSERT_OK(b_->GetFileSize("/dir/f", &file_size));
+  ASSERT_EQ(3U, file_size);
+
+  // Check that renaming works.
+  ASSERT_TRUE(!env_->RenameFile("/dir/non_existent", "/dir/g").ok());
+  ASSERT_OK(env_->RenameFile("/dir/f", "/dir/g"));
+  ASSERT_EQ(Status::NotFound(), env_->FileExists("/dir/f"));
+  ASSERT_OK(env_->FileExists("/dir/g"));
+  ASSERT_OK(env_->GetFileSize("/dir/g", &file_size));
+  ASSERT_EQ(3U, file_size);
+  ASSERT_OK(a_->FileExists("/dir/g"));
+  ASSERT_OK(a_->GetFileSize("/dir/g", &file_size));
+  ASSERT_EQ(3U, file_size);
+  ASSERT_OK(b_->FileExists("/dir/g"));
+  ASSERT_OK(b_->GetFileSize("/dir/g", &file_size));
+  ASSERT_EQ(3U, file_size);
+
+  // Check that opening non-existent file fails.
+  unique_ptr<SequentialFile> seq_file;
+  unique_ptr<RandomAccessFile> rand_file;
+  ASSERT_TRUE(
+      !env_->NewSequentialFile("/dir/non_existent", &seq_file, soptions_).ok());
+  ASSERT_TRUE(!seq_file);
+  ASSERT_TRUE(!env_->NewRandomAccessFile("/dir/non_existent", &rand_file,
+                                         soptions_).ok());
+  ASSERT_TRUE(!rand_file);
+
+  // Check that deleting works.
+  ASSERT_TRUE(!env_->DeleteFile("/dir/non_existent").ok());
+  ASSERT_OK(env_->DeleteFile("/dir/g"));
+  ASSERT_EQ(Status::NotFound(), env_->FileExists("/dir/g"));
+  ASSERT_OK(env_->GetChildren("/dir", &children));
+  ASSERT_EQ(0U, children.size());
+  ASSERT_OK(env_->DeleteDir("/dir"));
+}
+
+TEST_F(EnvMirrorTest, ReadWrite) {
+  unique_ptr<WritableFile> writable_file;
+  unique_ptr<SequentialFile> seq_file;
+  unique_ptr<RandomAccessFile> rand_file;
+  Slice result;
+  char scratch[100];
+
+  ASSERT_OK(env_->CreateDir("/dir"));
+
+  ASSERT_OK(env_->NewWritableFile("/dir/f", &writable_file, soptions_));
+  ASSERT_OK(writable_file->Append("hello "));
+  ASSERT_OK(writable_file->Append("world"));
+  writable_file.reset();
+
+  // Read sequentially.
+  ASSERT_OK(env_->NewSequentialFile("/dir/f", &seq_file, soptions_));
+  ASSERT_OK(seq_file->Read(5, &result, scratch));  // Read "hello".
+  ASSERT_EQ(0, result.compare("hello"));
+  ASSERT_OK(seq_file->Skip(1));
+  ASSERT_OK(seq_file->Read(1000, &result, scratch));  // Read "world".
+  ASSERT_EQ(0, result.compare("world"));
+  ASSERT_OK(seq_file->Read(1000, &result, scratch));  // Try reading past EOF.
+  ASSERT_EQ(0U, result.size());
+  ASSERT_OK(seq_file->Skip(100));  // Try to skip past end of file.
+  ASSERT_OK(seq_file->Read(1000, &result, scratch));
+  ASSERT_EQ(0U, result.size());
+
+  // Random reads.
+  ASSERT_OK(env_->NewRandomAccessFile("/dir/f", &rand_file, soptions_));
+  ASSERT_OK(rand_file->Read(6, 5, &result, scratch));  // Read "world".
+  ASSERT_EQ(0, result.compare("world"));
+  ASSERT_OK(rand_file->Read(0, 5, &result, scratch));  // Read "hello".
+  ASSERT_EQ(0, result.compare("hello"));
+  ASSERT_OK(rand_file->Read(10, 100, &result, scratch));  // Read "d".
+  ASSERT_EQ(0, result.compare("d"));
+
+  // Too high offset.
+  ASSERT_TRUE(!rand_file->Read(1000, 5, &result, scratch).ok());
+}
+
+TEST_F(EnvMirrorTest, Locks) {
+  FileLock* lock;
+
+  // These are no-ops, but we test they return success.
+  ASSERT_OK(env_->LockFile("some file", &lock));
+  ASSERT_OK(env_->UnlockFile(lock));
+}
+
+TEST_F(EnvMirrorTest, Misc) {
+  std::string test_dir;
+  ASSERT_OK(env_->GetTestDirectory(&test_dir));
+  ASSERT_TRUE(!test_dir.empty());
+
+  unique_ptr<WritableFile> writable_file;
+  ASSERT_OK(env_->NewWritableFile("/a/b", &writable_file, soptions_));
+
+  // These are no-ops, but we test they return success.
+  ASSERT_OK(writable_file->Sync());
+  ASSERT_OK(writable_file->Flush());
+  ASSERT_OK(writable_file->Close());
+  writable_file.reset();
+}
+
+TEST_F(EnvMirrorTest, LargeWrite) {
+  const size_t kWriteSize = 300 * 1024;
+  char* scratch = new char[kWriteSize * 2];
+
+  std::string write_data;
+  for (size_t i = 0; i < kWriteSize; ++i) {
+    write_data.append(1, static_cast<char>(i));
+  }
+
+  unique_ptr<WritableFile> writable_file;
+  ASSERT_OK(env_->NewWritableFile("/dir/f", &writable_file, soptions_));
+  ASSERT_OK(writable_file->Append("foo"));
+  ASSERT_OK(writable_file->Append(write_data));
+  writable_file.reset();
+
+  unique_ptr<SequentialFile> seq_file;
+  Slice result;
+  ASSERT_OK(env_->NewSequentialFile("/dir/f", &seq_file, soptions_));
+  ASSERT_OK(seq_file->Read(3, &result, scratch));  // Read "foo".
+  ASSERT_EQ(0, result.compare("foo"));
+
+  size_t read = 0;
+  std::string read_data;
+  while (read < kWriteSize) {
+    ASSERT_OK(seq_file->Read(kWriteSize - read, &result, scratch));
+    read_data.append(result.data(), result.size());
+    read += result.size();
+  }
+  ASSERT_TRUE(write_data == read_data);
+  delete[] scratch;
+}
+
+}  // namespace rocksdb
+
+int main(int argc, char** argv) {
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}
+
+#else
+#include <stdio.h>
+
+int main(int argc, char** argv) {
+  fprintf(stderr, "SKIPPED as EnvMirror is not supported in ROCKSDB_LITE\n");
+  return 0;
+}
+
+#endif  // !ROCKSDB_LITE