diff --git a/cmd/cachefs/main.go b/cmd/cachefs/main.go
index a32ff9d..aad2c37 100644
--- a/cmd/cachefs/main.go
+++ b/cmd/cachefs/main.go
@@ -30,6 +30,7 @@ var (
 	listenCache  string
 	quota        int64
 	max          int
+	bs           int
 
 	log logr.Logger
 )
@@ -45,12 +46,17 @@ func main() {
 	flag.StringVar(&listenWebdav, "webdav", "", "listen addr:port for webdav")
 	flag.StringVar(&listenCache, "cache", "", "listen addr:port for cache only")
 	flag.IntVar(&max, "max", -1, "max parallel preloads")
+	flag.IntVar(&bs, "bs", -1, "tune reload buffer size in bytes (default: 8192)")
 	flag.Int64Var(&quota, "quota", 1, "max disk usage quota in GiB")
 	flag.Parse()
 
 	log = klogr.New().WithName("main")
 	log.Info("starting cachefs", "version", version)
 
+	if fs.SetBufferSize(bs) {
+		log.V(2).Info("changed preload buffer size", "size", bs)
+	}
+
 	filesystem, err := fs.NewFS(quota*gib, max, src, dst, metadata, klogr.New().WithName("fs"))
 	if err != nil {
 		klog.Fatalf("init failed: %s", err)
diff --git a/pkg/fs/discard.go b/pkg/fs/discard.go
new file mode 100644
index 0000000..fdf049d
--- /dev/null
+++ b/pkg/fs/discard.go
@@ -0,0 +1,60 @@
+// Copyright (C) 2022 Marius Schellenberger
+
+package fs
+
+import (
+	"io"
+	"sync"
+)
+
+var Discard io.Writer = discard{}
+
+type discard struct{}
+
+var _ io.ReaderFrom = discard{}
+
+func (discard) Write(p []byte) (int, error) {
+	return len(p), nil
+}
+
+func (discard) WriteString(s string) (int, error) {
+	return len(s), nil
+}
+
+const DefaultBufferSize = 8192
+
+var blackHolePool = sync.Pool{
+	New: func() any {
+		b := make([]byte, DefaultBufferSize)
+		return &b
+	},
+}
+
+func SetBufferSize(size int) bool {
+	if size < 0 || size == DefaultBufferSize {
+		return false
+	}
+	blackHolePool = sync.Pool{
+		New: func() any {
+			b := make([]byte, size)
+			return &b
+		},
+	}
+	return true
+}
+
+func (discard) ReadFrom(r io.Reader) (n int64, err error) {
+	bufp := blackHolePool.Get().(*[]byte)
+	readSize := 0
+	for {
+		readSize, err = r.Read(*bufp)
+		n += int64(readSize)
+		if err != nil {
+			blackHolePool.Put(bufp)
+			if err == io.EOF {
+				return n, nil
+			}
+			return
+		}
+	}
+}
diff --git a/pkg/fs/file.go b/pkg/fs/file.go
index 17356b4..33400d9 100644
--- a/pkg/fs/file.go
+++ b/pkg/fs/file.go
@@ -41,31 +41,33 @@ func (p *preload) Read(data []byte) (n int, err error) {
 		_, err = p.f.Seek(int64(n), io.SeekCurrent)
 		return
 	}
-	n, err = p.f.readWithoutCache(data)
+	n, err = p.f.readToCache(data)
 	p.written++
 	return
 }
 
 func (f *File) Preload(ctx context.Context, unlock func()) {
 	log := f.log
+	defer unlock()
 	if f.offline {
 		log.V(2).Error(errors.New("no preload in offline mode"), "error preloading file")
-		unlock()
+		return
+	}
+	if f.md.FullyCached() {
+		log.V(2).Info("skipped preload for fully cached file")
 		return
 	}
 	log.V(2).Info("preload started")
 	p := &preload{f: f, ctx: ctx}
-	_, err := io.Copy(io.Discard, p)
+	_, err := io.Copy(Discard, p)
 	if err == context.Canceled {
 		log.V(2).Info("preload canceled", "skipped", p.skipped, "written", p.written)
-		unlock()
 		return
 	}
 	if err != nil && err != io.EOF {
 		log.Error(err, "error preloading file")
 	}
 	log.V(2).Info("preload finished", "skipped", p.skipped, "written", p.written)
-	unlock()
 }
 
 func (f *File) Read(p []byte) (n int, err error) {
@@ -73,8 +75,15 @@ func (f *File) Read(p []byte) (n int, err error) {
 	if f.hasChunk(len(p)) {
 		n, err = f.md.ReadAt(p, f.offset)
 		if err != nil {
-			log.Error(err, "error reading cache file")
-			return
+			if !IsIOErr(err) {
+				log.Error(err, "error reading cache file")
+				return
+			}
+			n, err = f.readSource(p)
+			if err != nil {
+				log.Error(err, "error reading source file")
+				return
+			}
 		}
 		_, err = f.Seek(int64(n), io.SeekCurrent)
 		if err != nil {
@@ -82,7 +91,7 @@ func (f *File) Read(p []byte) (n int, err error) {
 		}
 		return
 	}
-	return f.readWithoutCache(p)
+	return f.readToCache(p)
 }
 
 func (f *File) size() int64 {
@@ -93,12 +102,16 @@ func (f *File) hasChunk(n int) bool {
 	return f.md.HasChunk(f.offset, n)
 }
 
-func (f *File) readWithoutCache(p []byte) (n int, err error) {
+func (f *File) readSource(p []byte) (n int, err error) {
 	if f.offline {
 		return 0, io.EOF
 	}
+	return f.f.Read(p)
+}
+
+func (f *File) readToCache(p []byte) (n int, err error) {
 	log := f.log
-	n, err = f.f.Read(p)
+	n, err = f.readSource(p)
 	if n > 0 {
 		if n, err := f.md.WriteAt(p[:n], f.offset); err != nil {
 			log.Error(err, "error writing cache file")
diff --git a/pkg/fs/metadata.go b/pkg/fs/metadata.go
index a7ee420..8e4b57a 100644
--- a/pkg/fs/metadata.go
+++ b/pkg/fs/metadata.go
@@ -273,6 +273,31 @@ func (mh *MetadataHandler) close() {
 	close(mh.fs.done)
 }
 
+type Error string
+
+func (e Error) Error() string {
+	return string(e)
+}
+
+const (
+	IOErr Error = "input/output error"
+)
+
+func MapError(err error) error {
+	if err == nil {
+		return nil
+	}
+	s := err.Error()
+	if strings.HasSuffix(s, IOErr.Error()) {
+		return IOErr
+	}
+	return nil
+}
+
+func IsIOErr(err error) bool {
+	return MapError(err) == IOErr
+}
+
 type Metadata struct {
 	mu     sync.RWMutex `json:"-"`
 	fs     *FS          `json:"-"`
@@ -293,6 +318,15 @@ func (md *Metadata) Delete() error {
 	return md.fs.RemoveDst(md.name)
 }
 
+func (md *Metadata) FullyCached() bool {
+	md.mu.RLock()
+	defer md.mu.RUnlock()
+	if len(md.Chunks) == 0 {
+		return false
+	}
+	return md.Size == md.Chunks[0][1]
+}
+
 func (md *Metadata) HasChunk(off int64, n int) bool {
 	md.mu.RLock()
 	defer md.mu.RUnlock()