From 76e2713ffe5f54fda843449e1d9bb7a169907f5d Mon Sep 17 00:00:00 2001
From: Harshavardhana <harsha@minio.io>
Date: Wed, 6 Jan 2021 09:36:55 -0800
Subject: [PATCH] fix: use buffers only when necessary for io.Copy() (#11229)

Use separate sync.Pool for writes/reads

Avoid passing buffers for io.CopyBuffer()
if the writer or reader implement io.WriteTo or io.ReadFrom
respectively then its useless for sync.Pool to allocate
buffers on its own since that will be completely ignored
by the io.CopyBuffer Go implementation.

Improve this wherever we see this to be optimal.

This allows us to be more efficient on memory usage.
```
   385  // copyBuffer is the actual implementation of Copy and CopyBuffer.
   386  // if buf is nil, one is allocated.
   387  func copyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) {
   388  	// If the reader has a WriteTo method, use it to do the copy.
   389  	// Avoids an allocation and a copy.
   390  	if wt, ok := src.(WriterTo); ok {
   391  		return wt.WriteTo(dst)
   392  	}
   393  	// Similarly, if the writer has a ReadFrom method, use it to do the copy.
   394  	if rt, ok := dst.(ReaderFrom); ok {
   395  		return rt.ReadFrom(src)
   396  	}
```

From readahead package
```
// WriteTo writes data to w until there's no more data to write or when an error occurs.
// The return value n is the number of bytes written.
// Any error encountered during the write is also returned.
func (a *reader) WriteTo(w io.Writer) (n int64, err error) {
	if a.err != nil {
		return 0, a.err
	}
	n = 0
	for {
		err = a.fill()
		if err != nil {
			return n, err
		}
		n2, err := w.Write(a.cur.buffer())
		a.cur.inc(n2)
		n += int64(n2)
		if err != nil {
			return n, err
		}
```
---
 buildscripts/race.sh                |   2 +-
 cmd/fs-v1-helpers.go                |  23 ++---
 cmd/fs-v1-helpers_test.go           |  19 ++---
 cmd/fs-v1-multipart.go              |   8 +-
 cmd/fs-v1.go                        |  19 +----
 cmd/handler-api.go                  |   2 +-
 cmd/object-api-common.go            |   3 -
 cmd/storage-rest-server.go          |  10 +--
 cmd/xl-storage.go                   | 126 +++++++++-------------------
 cmd/xl-storage_test.go              |   9 +-
 docs/shared-backend/DESIGN.md       |   2 +-
 docs/zh_CN/shared-backend/DESIGN.md |   4 +-
 pkg/ioutil/append-file_nix.go       |   4 +-
 pkg/ioutil/append-file_windows.go   |   4 +-
 pkg/ioutil/ioutil.go                |   6 +-
 15 files changed, 71 insertions(+), 170 deletions(-)

diff --git a/buildscripts/race.sh b/buildscripts/race.sh
index 66ee3de4a..7c34510ea 100755
--- a/buildscripts/race.sh
+++ b/buildscripts/race.sh
@@ -3,5 +3,5 @@
 set -e
 
 for d in $(go list ./... | grep -v browser); do
-    CGO_ENABLED=1 go test -v -race --timeout 50m "$d"
+    CGO_ENABLED=1 go test -v -race --timeout 100m "$d"
 done
diff --git a/cmd/fs-v1-helpers.go b/cmd/fs-v1-helpers.go
index 7009a3ed0..4aa216a38 100644
--- a/cmd/fs-v1-helpers.go
+++ b/cmd/fs-v1-helpers.go
@@ -271,8 +271,8 @@ func fsOpenFile(ctx context.Context, readPath string, offset int64) (io.ReadClos
 	return fr, st.Size(), nil
 }
 
-// Creates a file and copies data from incoming reader. Staging buffer is used by io.CopyBuffer.
-func fsCreateFile(ctx context.Context, filePath string, reader io.Reader, buf []byte, fallocSize int64) (int64, error) {
+// Creates a file and copies data from incoming reader.
+func fsCreateFile(ctx context.Context, filePath string, reader io.Reader, fallocSize int64) (int64, error) {
 	if filePath == "" || reader == nil {
 		logger.LogIf(ctx, errInvalidArgument)
 		return 0, errInvalidArgument
@@ -317,21 +317,10 @@ func fsCreateFile(ctx context.Context, filePath string, reader io.Reader, buf []
 		}
 	}
 
-	var bytesWritten int64
-	if buf != nil {
-		bytesWritten, err = io.CopyBuffer(writer, reader, buf)
-		if err != nil {
-			if err != io.ErrUnexpectedEOF {
-				logger.LogIf(ctx, err)
-			}
-			return 0, err
-		}
-	} else {
-		bytesWritten, err = io.Copy(writer, reader)
-		if err != nil {
-			logger.LogIf(ctx, err)
-			return 0, err
-		}
+	bytesWritten, err := io.Copy(writer, reader)
+	if err != nil {
+		logger.LogIf(ctx, err)
+		return 0, err
 	}
 
 	return bytesWritten, nil
diff --git a/cmd/fs-v1-helpers_test.go b/cmd/fs-v1-helpers_test.go
index 8344b913d..b2f42978f 100644
--- a/cmd/fs-v1-helpers_test.go
+++ b/cmd/fs-v1-helpers_test.go
@@ -75,7 +75,7 @@ func TestFSStats(t *testing.T) {
 	}
 
 	var reader = bytes.NewReader([]byte("Hello, world"))
-	if _, err = fsCreateFile(GlobalContext, pathJoin(path, "success-vol", "success-file"), reader, nil, 0); err != nil {
+	if _, err = fsCreateFile(GlobalContext, pathJoin(path, "success-vol", "success-file"), reader, 0); err != nil {
 		t.Fatalf("Unable to create file, %s", err)
 	}
 	// Seek back.
@@ -85,7 +85,7 @@ func TestFSStats(t *testing.T) {
 		t.Fatal("Unexpected error", err)
 	}
 
-	if _, err = fsCreateFile(GlobalContext, pathJoin(path, "success-vol", "path/to/success-file"), reader, nil, 0); err != nil {
+	if _, err = fsCreateFile(GlobalContext, pathJoin(path, "success-vol", "path/to/success-file"), reader, 0); err != nil {
 		t.Fatalf("Unable to create file, %s", err)
 	}
 	// Seek back.
@@ -192,7 +192,7 @@ func TestFSCreateAndOpen(t *testing.T) {
 		t.Fatalf("Unable to create directory, %s", err)
 	}
 
-	if _, err = fsCreateFile(GlobalContext, "", nil, nil, 0); err != errInvalidArgument {
+	if _, err = fsCreateFile(GlobalContext, "", nil, 0); err != errInvalidArgument {
 		t.Fatal("Unexpected error", err)
 	}
 
@@ -201,7 +201,7 @@ func TestFSCreateAndOpen(t *testing.T) {
 	}
 
 	var reader = bytes.NewReader([]byte("Hello, world"))
-	if _, err = fsCreateFile(GlobalContext, pathJoin(path, "success-vol", "success-file"), reader, nil, 0); err != nil {
+	if _, err = fsCreateFile(GlobalContext, pathJoin(path, "success-vol", "success-file"), reader, 0); err != nil {
 		t.Fatalf("Unable to create file, %s", err)
 	}
 	// Seek back.
@@ -229,7 +229,7 @@ func TestFSCreateAndOpen(t *testing.T) {
 	}
 
 	for i, testCase := range testCases {
-		_, err = fsCreateFile(GlobalContext, pathJoin(path, testCase.srcVol, testCase.srcPath), reader, nil, 0)
+		_, err = fsCreateFile(GlobalContext, pathJoin(path, testCase.srcVol, testCase.srcPath), reader, 0)
 		if err != testCase.expectedErr {
 			t.Errorf("Test case %d: Expected: \"%s\", got: \"%s\"", i+1, testCase.expectedErr, err)
 		}
@@ -258,9 +258,8 @@ func TestFSDeletes(t *testing.T) {
 		t.Fatalf("Unable to create directory, %s", err)
 	}
 
-	var buf = make([]byte, 4096)
 	var reader = bytes.NewReader([]byte("Hello, world"))
-	if _, err = fsCreateFile(GlobalContext, pathJoin(path, "success-vol", "success-file"), reader, buf, reader.Size()); err != nil {
+	if _, err = fsCreateFile(GlobalContext, pathJoin(path, "success-vol", "success-file"), reader, reader.Size()); err != nil {
 		t.Fatalf("Unable to create file, %s", err)
 	}
 	// Seek back.
@@ -396,13 +395,13 @@ func TestFSRemoves(t *testing.T) {
 	}
 
 	var reader = bytes.NewReader([]byte("Hello, world"))
-	if _, err = fsCreateFile(GlobalContext, pathJoin(path, "success-vol", "success-file"), reader, nil, 0); err != nil {
+	if _, err = fsCreateFile(GlobalContext, pathJoin(path, "success-vol", "success-file"), reader, 0); err != nil {
 		t.Fatalf("Unable to create file, %s", err)
 	}
 	// Seek back.
 	reader.Seek(0, 0)
 
-	if _, err = fsCreateFile(GlobalContext, pathJoin(path, "success-vol", "success-file-new"), reader, nil, 0); err != nil {
+	if _, err = fsCreateFile(GlobalContext, pathJoin(path, "success-vol", "success-file-new"), reader, 0); err != nil {
 		t.Fatalf("Unable to create file, %s", err)
 	}
 	// Seek back.
@@ -515,7 +514,7 @@ func TestFSRemoveMeta(t *testing.T) {
 	filePath := pathJoin(fsPath, "success-vol", "success-file")
 
 	var reader = bytes.NewReader([]byte("Hello, world"))
-	if _, err = fsCreateFile(GlobalContext, filePath, reader, nil, 0); err != nil {
+	if _, err = fsCreateFile(GlobalContext, filePath, reader, 0); err != nil {
 		t.Fatalf("Unable to create file, %s", err)
 	}
 
diff --git a/cmd/fs-v1-multipart.go b/cmd/fs-v1-multipart.go
index e1061c961..7744c07b4 100644
--- a/cmd/fs-v1-multipart.go
+++ b/cmd/fs-v1-multipart.go
@@ -313,14 +313,8 @@ func (fs *FSObjects) PutObjectPart(ctx context.Context, bucket, object, uploadID
 		return pi, toObjectErr(err, bucket, object)
 	}
 
-	bufSize := int64(readSizeV1)
-	if size := data.Size(); size > 0 && bufSize > size {
-		bufSize = size
-	}
-	buf := make([]byte, bufSize)
-
 	tmpPartPath := pathJoin(fs.fsPath, minioMetaTmpBucket, fs.fsUUID, uploadID+"."+mustGetUUID()+"."+strconv.Itoa(partID))
-	bytesWritten, err := fsCreateFile(ctx, tmpPartPath, data, buf, data.Size())
+	bytesWritten, err := fsCreateFile(ctx, tmpPartPath, data, data.Size())
 
 	// Delete temporary part in case of failure. If
 	// PutObjectPart succeeds then there would be nothing to
diff --git a/cmd/fs-v1.go b/cmd/fs-v1.go
index e5e3281d7..4517f9374 100644
--- a/cmd/fs-v1.go
+++ b/cmd/fs-v1.go
@@ -857,11 +857,6 @@ func (fs *FSObjects) getObject(ctx context.Context, bucket, object string, offse
 	}
 	defer reader.Close()
 
-	bufSize := int64(readSizeV1)
-	if length > 0 && bufSize > length {
-		bufSize = length
-	}
-
 	// For negative length we read everything.
 	if length < 0 {
 		length = size - offset
@@ -874,10 +869,7 @@ func (fs *FSObjects) getObject(ctx context.Context, bucket, object string, offse
 		return err
 	}
 
-	// Allocate a staging buffer.
-	buf := make([]byte, int(bufSize))
-
-	_, err = io.CopyBuffer(writer, io.LimitReader(reader, length), buf)
+	_, err = io.Copy(writer, io.LimitReader(reader, length))
 	// The writer will be closed incase of range queries, which will emit ErrClosedPipe.
 	if err == io.ErrClosedPipe {
 		err = nil
@@ -1199,15 +1191,8 @@ func (fs *FSObjects) putObject(ctx context.Context, bucket string, object string
 	// so that cleaning it up will be easy if the server goes down.
 	tempObj := mustGetUUID()
 
-	// Allocate a buffer to Read() from request body
-	bufSize := int64(readSizeV1)
-	if size := data.Size(); size > 0 && bufSize > size {
-		bufSize = size
-	}
-
-	buf := make([]byte, int(bufSize))
 	fsTmpObjPath := pathJoin(fs.fsPath, minioMetaTmpBucket, fs.fsUUID, tempObj)
-	bytesWritten, err := fsCreateFile(ctx, fsTmpObjPath, data, buf, data.Size())
+	bytesWritten, err := fsCreateFile(ctx, fsTmpObjPath, data, data.Size())
 
 	// Delete the temporary object in the case of a
 	// failure. If PutObject succeeds, then there would be
diff --git a/cmd/handler-api.go b/cmd/handler-api.go
index 849ea2986..3f98884ac 100644
--- a/cmd/handler-api.go
+++ b/cmd/handler-api.go
@@ -57,7 +57,7 @@ func (t *apiConfig) init(cfg api.Config, setDriveCount int) {
 		// max requests per node is calculated as
 		// total_ram / ram_per_request
 		// ram_per_request is 4MiB * setDriveCount + 2 * 10MiB (default erasure block size)
-		apiRequestsMaxPerNode = int(stats.TotalRAM / uint64(setDriveCount*readBlockSize+blockSizeV1*2))
+		apiRequestsMaxPerNode = int(stats.TotalRAM / uint64(setDriveCount*(writeBlockSize+readBlockSize)+blockSizeV1*2))
 	} else {
 		apiRequestsMaxPerNode = cfg.RequestsMax
 		if len(globalEndpoints.Hostnames()) > 0 {
diff --git a/cmd/object-api-common.go b/cmd/object-api-common.go
index e278ad3dc..d4ab9646d 100644
--- a/cmd/object-api-common.go
+++ b/cmd/object-api-common.go
@@ -31,9 +31,6 @@ const (
 	// Block size used for all internal operations version 1.
 	blockSizeV1 = 10 * humanize.MiByte
 
-	// Staging buffer read size for all internal operations version 1.
-	readSizeV1 = 1 * humanize.MiByte
-
 	// Buckets meta prefix.
 	bucketMetaPrefix = "buckets"
 
diff --git a/cmd/storage-rest-server.go b/cmd/storage-rest-server.go
index 01c050d7d..9d806ba81 100644
--- a/cmd/storage-rest-server.go
+++ b/cmd/storage-rest-server.go
@@ -515,15 +515,7 @@ func (s *storageRESTServer) ReadFileStreamHandler(w http.ResponseWriter, r *http
 	defer rc.Close()
 
 	w.Header().Set(xhttp.ContentLength, strconv.Itoa(length))
-
-	if length >= readBlockSize {
-		bufp := s.storage.pool.Get().(*[]byte)
-		defer s.storage.pool.Put(bufp)
-
-		io.CopyBuffer(w, rc, *bufp)
-	} else {
-		io.Copy(w, rc)
-	}
+	io.Copy(w, rc)
 	w.(http.Flusher).Flush()
 }
 
diff --git a/cmd/xl-storage.go b/cmd/xl-storage.go
index a896f987e..6418f50f1 100644
--- a/cmd/xl-storage.go
+++ b/cmd/xl-storage.go
@@ -55,7 +55,8 @@ import (
 const (
 	nullVersionID     = "null"
 	diskMinTotalSpace = 900 * humanize.MiByte // Min 900MiB total space.
-	readBlockSize     = 4 * humanize.MiByte   // Default read block size 4MiB.
+	writeBlockSize    = 4 * humanize.MiByte   // Default write block size 4MiB.
+	readBlockSize     = 2 * humanize.MiByte   // Default read block size 2MiB.
 
 	// On regular files bigger than this;
 	readAheadSize = 16 << 20
@@ -90,10 +91,11 @@ type xlStorage struct {
 	diskPath string
 	endpoint Endpoint
 
-	pool sync.Pool
-
 	globalSync bool
 
+	wpool sync.Pool
+	rpool sync.Pool
+
 	rootDisk bool
 
 	diskID string
@@ -254,7 +256,13 @@ func newXLStorage(ep Endpoint) (*xlStorage, error) {
 	p := &xlStorage{
 		diskPath: path,
 		endpoint: ep,
-		pool: sync.Pool{
+		wpool: sync.Pool{
+			New: func() interface{} {
+				b := disk.AlignedBlock(writeBlockSize)
+				return &b
+			},
+		},
+		rpool: sync.Pool{
 			New: func() interface{} {
 				b := disk.AlignedBlock(readBlockSize)
 				return &b
@@ -671,12 +679,16 @@ func (s *xlStorage) StatVol(ctx context.Context, volume string) (vol VolInfo, er
 	var st os.FileInfo
 	st, err = os.Stat(volumeDir)
 	if err != nil {
-		if osIsNotExist(err) {
+		switch {
+		case osIsNotExist(err):
 			return VolInfo{}, errVolumeNotFound
-		} else if isSysErrIO(err) {
+		case osIsPermission(err):
+			return VolInfo{}, errDiskAccessDenied
+		case isSysErrIO(err):
 			return VolInfo{}, errFaultyDisk
+		default:
+			return VolInfo{}, err
 		}
-		return VolInfo{}, err
 	}
 	// As os.Stat() doesn't carry other than ModTime(), use ModTime()
 	// as CreatedTime.
@@ -723,58 +735,6 @@ func (s *xlStorage) DeleteVol(ctx context.Context, volume string, forceDelete bo
 	return nil
 }
 
-const guidSplunk = "guidSplunk"
-
-// ListDirSplunk - return all the entries at the given directory path.
-// If an entry is a directory it will be returned with a trailing SlashSeparator.
-func (s *xlStorage) ListDirSplunk(volume, dirPath string, count int) (entries []string, err error) {
-	guidIndex := strings.Index(dirPath, guidSplunk)
-	if guidIndex != -1 {
-		return nil, nil
-	}
-
-	atomic.AddInt32(&s.activeIOCount, 1)
-	defer func() {
-		atomic.AddInt32(&s.activeIOCount, -1)
-	}()
-
-	// Verify if volume is valid and it exists.
-	volumeDir, err := s.getVolDir(volume)
-	if err != nil {
-		return nil, err
-	}
-
-	if _, err = os.Stat(volumeDir); err != nil {
-		if osIsNotExist(err) {
-			return nil, errVolumeNotFound
-		} else if isSysErrIO(err) {
-			return nil, errFaultyDisk
-		}
-		return nil, err
-	}
-
-	dirPathAbs := pathJoin(volumeDir, dirPath)
-	if count > 0 {
-		entries, err = readDirN(dirPathAbs, count)
-	} else {
-		entries, err = readDir(dirPathAbs)
-	}
-	if err != nil {
-		return nil, err
-	}
-
-	return entries, nil
-}
-
-func (s *xlStorage) isLeafSplunk(volume string, leafPath string) bool {
-	const receiptJSON = "receipt.json"
-
-	if path.Base(leafPath) != receiptJSON {
-		return false
-	}
-	return s.isLeaf(volume, leafPath)
-}
-
 func (s *xlStorage) isLeaf(volume string, leafPath string) bool {
 	volumeDir, err := s.getVolDir(volume)
 	if err != nil {
@@ -903,15 +863,6 @@ func (s *xlStorage) ListDir(ctx context.Context, volume, dirPath string, count i
 		return nil, err
 	}
 
-	if _, err = os.Stat(volumeDir); err != nil {
-		if osIsNotExist(err) {
-			return nil, errVolumeNotFound
-		} else if isSysErrIO(err) {
-			return nil, errFaultyDisk
-		}
-		return nil, err
-	}
-
 	dirPathAbs := pathJoin(volumeDir, dirPath)
 	if count > 0 {
 		entries, err = readDirN(dirPathAbs, count)
@@ -919,6 +870,15 @@ func (s *xlStorage) ListDir(ctx context.Context, volume, dirPath string, count i
 		entries, err = readDir(dirPathAbs)
 	}
 	if err != nil {
+		if err == errFileNotFound {
+			if _, verr := os.Stat(volumeDir); verr != nil {
+				if osIsNotExist(verr) {
+					return nil, errVolumeNotFound
+				} else if isSysErrIO(verr) {
+					return nil, errFaultyDisk
+				}
+			}
+		}
 		return nil, err
 	}
 
@@ -1122,8 +1082,6 @@ func (s *xlStorage) renameLegacyMetadata(volume, path string) error {
 }
 
 // ReadVersion - reads metadata and returns FileInfo at path `xl.meta`
-// for all objects less than `128KiB` this call returns data as well
-// along with metadata.
 func (s *xlStorage) ReadVersion(ctx context.Context, volume, path, versionID string) (fi FileInfo, err error) {
 	buf, err := s.ReadAll(ctx, volume, pathJoin(path, xlStorageFormatFile))
 	if err != nil {
@@ -1300,11 +1258,8 @@ func (s *xlStorage) ReadFile(ctx context.Context, volume string, path string, of
 		return int64(n), err
 	}
 
-	bufp := s.pool.Get().(*[]byte)
-	defer s.pool.Put(bufp)
-
 	h := verifier.algorithm.New()
-	if _, err = io.CopyBuffer(h, io.LimitReader(file, offset), *bufp); err != nil {
+	if _, err = io.Copy(h, io.LimitReader(file, offset)); err != nil {
 		return 0, err
 	}
 
@@ -1316,7 +1271,7 @@ func (s *xlStorage) ReadFile(ctx context.Context, volume string, path string, of
 		return 0, err
 	}
 
-	if _, err = io.CopyBuffer(h, file, *bufp); err != nil {
+	if _, err = io.Copy(h, file); err != nil {
 		return 0, err
 	}
 
@@ -1384,7 +1339,7 @@ func (s *xlStorage) openFile(volume, path string, mode int) (f *os.File, err err
 }
 
 // To support O_DIRECT reads for erasure backends.
-type odirectreader struct {
+type odirectReader struct {
 	f         *os.File
 	buf       []byte
 	bufp      *[]byte
@@ -1394,12 +1349,12 @@ type odirectreader struct {
 }
 
 // Read - Implements Reader interface.
-func (o *odirectreader) Read(buf []byte) (n int, err error) {
+func (o *odirectReader) Read(buf []byte) (n int, err error) {
 	if o.err != nil {
 		return 0, o.err
 	}
 	if o.buf == nil {
-		o.bufp = o.s.pool.Get().(*[]byte)
+		o.bufp = o.s.rpool.Get().(*[]byte)
 	}
 	if o.freshRead {
 		o.buf = *o.bufp
@@ -1427,8 +1382,8 @@ func (o *odirectreader) Read(buf []byte) (n int, err error) {
 }
 
 // Close - Release the buffer and close the file.
-func (o *odirectreader) Close() error {
-	o.s.pool.Put(o.bufp)
+func (o *odirectReader) Close() error {
+	o.s.rpool.Put(o.bufp)
 	atomic.AddInt32(&o.s.activeIOCount, -1)
 	return o.f.Close()
 }
@@ -1474,7 +1429,7 @@ func (s *xlStorage) ReadFileStream(ctx context.Context, volume, path string, off
 		}
 
 		atomic.AddInt32(&s.activeIOCount, 1)
-		return &odirectreader{file, nil, nil, true, s, nil}, nil
+		return &odirectReader{file, nil, nil, true, s, nil}, nil
 	}
 
 	// Open the file for reading.
@@ -1640,8 +1595,8 @@ func (s *xlStorage) CreateFile(ctx context.Context, volume, path string, fileSiz
 		w.Close()
 	}()
 
-	bufp := s.pool.Get().(*[]byte)
-	defer s.pool.Put(bufp)
+	bufp := s.wpool.Get().(*[]byte)
+	defer s.wpool.Put(bufp)
 
 	written, err := xioutil.CopyAligned(w, r, *bufp, fileSize)
 	if err != nil {
@@ -2271,11 +2226,8 @@ func (s *xlStorage) bitrotVerify(partPath string, partSize int64, algo BitrotAlg
 	defer file.Close()
 
 	if algo != HighwayHash256S {
-		bufp := s.pool.Get().(*[]byte)
-		defer s.pool.Put(bufp)
-
 		h := algo.New()
-		if _, err = io.CopyBuffer(h, file, *bufp); err != nil {
+		if _, err = io.Copy(h, file); err != nil {
 			// Premature failure in reading the object,file is corrupt.
 			return errFileCorrupt
 		}
diff --git a/cmd/xl-storage_test.go b/cmd/xl-storage_test.go
index 97ec5eb18..108d7c8fb 100644
--- a/cmd/xl-storage_test.go
+++ b/cmd/xl-storage_test.go
@@ -703,8 +703,8 @@ func TestXLStorageListVols(t *testing.T) {
 	}
 }
 
-// TestXLStorageXlStorageListDir -  TestXLStorages validate the directory listing functionality provided by xlStorage.ListDir .
-func TestXLStorageXlStorageListDir(t *testing.T) {
+// TestXLStorageListDir -  TestXLStorages validate the directory listing functionality provided by xlStorage.ListDir .
+func TestXLStorageListDir(t *testing.T) {
 	// create xlStorage test setup
 	xlStorage, path, err := newXLStorageTestSetup()
 	if err != nil {
@@ -1692,8 +1692,9 @@ func TestXLStorageVerifyFile(t *testing.T) {
 	w := newStreamingBitrotWriter(xlStorage, volName, fileName, size, algo, shardSize)
 	reader := bytes.NewReader(data)
 	for {
-		// Using io.CopyBuffer instead of this loop will not work for us as io.CopyBuffer
-		// will use bytes.Buffer.ReadConfig() which will not do shardSize'ed writes causing error.
+		// Using io.Copy instead of this loop will not work for us as io.Copy
+		// will use bytes.Reader.WriteTo() which will not do shardSize'ed writes
+		// causing error.
 		n, err := reader.Read(shard)
 		w.Write(shard[:n])
 		if err == nil {
diff --git a/docs/shared-backend/DESIGN.md b/docs/shared-backend/DESIGN.md
index e50df2c19..b7220fffa 100644
--- a/docs/shared-backend/DESIGN.md
+++ b/docs/shared-backend/DESIGN.md
@@ -90,7 +90,7 @@ GetObject() holds a read lock on `fs.json`.
 
 ... you can perform other operations here ...
 
-	_, err = io.CopyBuffer(writer, reader, buf)
+	_, err = io.Copy(writer, reader)
 
 ... after successful copy operation unlocks the read lock ...
 ```
diff --git a/docs/zh_CN/shared-backend/DESIGN.md b/docs/zh_CN/shared-backend/DESIGN.md
index 4c51390ee..8757872ec 100644
--- a/docs/zh_CN/shared-backend/DESIGN.md
+++ b/docs/zh_CN/shared-backend/DESIGN.md
@@ -38,7 +38,7 @@ minio server /path/to/nfs-volume
 
 ### Windows 2012 Server
 
-示例1: 运行Minio实例在持载在`\\remote-server\cifs`路径下的共享后端存储。 
+示例1: 运行Minio实例在持载在`\\remote-server\cifs`路径下的共享后端存储。
 
 On windows server1
 ```cmd
@@ -94,7 +94,7 @@ GetObject()持有`fs.json`的一个读锁。
 
 ... you can perform other operations here ...
 
-	_, err = io.CopyBuffer(writer, reader, buf)
+	_, err = io.Copy(writer, reader)
 
 ... after successful copy operation unlocks the read lock ...
 ```
diff --git a/pkg/ioutil/append-file_nix.go b/pkg/ioutil/append-file_nix.go
index 468c185d0..3e60383dc 100644
--- a/pkg/ioutil/append-file_nix.go
+++ b/pkg/ioutil/append-file_nix.go
@@ -40,8 +40,6 @@ func AppendFile(dst string, src string, osync bool) error {
 		return err
 	}
 	defer srcFile.Close()
-	// Allocate staging buffer.
-	var buf = make([]byte, defaultAppendBufferSize)
-	_, err = io.CopyBuffer(appendFile, srcFile, buf)
+	_, err = io.Copy(appendFile, srcFile)
 	return err
 }
diff --git a/pkg/ioutil/append-file_windows.go b/pkg/ioutil/append-file_windows.go
index ee23bb03b..c93cb5fd5 100644
--- a/pkg/ioutil/append-file_windows.go
+++ b/pkg/ioutil/append-file_windows.go
@@ -36,8 +36,6 @@ func AppendFile(dst string, src string, osync bool) error {
 		return err
 	}
 	defer srcFile.Close()
-	// Allocate staging buffer.
-	var buf = make([]byte, defaultAppendBufferSize)
-	_, err = io.CopyBuffer(appendFile, srcFile, buf)
+	_, err = io.Copy(appendFile, srcFile)
 	return err
 }
diff --git a/pkg/ioutil/ioutil.go b/pkg/ioutil/ioutil.go
index 6c66c3859..d034c611d 100644
--- a/pkg/ioutil/ioutil.go
+++ b/pkg/ioutil/ioutil.go
@@ -22,13 +22,9 @@ import (
 	"io"
 	"os"
 
-	humanize "github.com/dustin/go-humanize"
 	"github.com/minio/minio/pkg/disk"
 )
 
-// defaultAppendBufferSize - Default buffer size for the AppendFile
-const defaultAppendBufferSize = humanize.MiByte
-
 // WriteOnCloser implements io.WriteCloser and always
 // executes at least one write operation if it is closed.
 //
@@ -186,7 +182,7 @@ const directioAlignSize = 4096
 // 4K page boundaries. Without passing aligned buffer may cause
 // this function to return error.
 //
-// This code is similar in spirit to io.CopyBuffer but it is only to be
+// This code is similar in spirit to io.Copy but it is only to be
 // used with DIRECT I/O based file descriptor and it is expected that
 // input writer *os.File not a generic io.Writer. Make sure to have
 // the file opened for writes with syscall.O_DIRECT flag.