Revert "volume: avoid file.stat(), file.seek() if possible during writes"

This reverts commit c78409a598.

weed/storage/needle_map.go

@@ -41,7 +41,6 @@ type baseNeedleMapper struct {
 
 	indexFile           *os.File
 	indexFileAccessLock sync.Mutex
-	indexFileOffset     int64
 }
 
 func (nm *baseNeedleMapper) IndexFileSize() uint64 {
@@ -57,18 +56,11 @@ func (nm *baseNeedleMapper) appendToIndexFile(key NeedleId, offset Offset, size
 
 	nm.indexFileAccessLock.Lock()
 	defer nm.indexFileAccessLock.Unlock()
-	if nm.indexFileOffset == 0 {
-		if fileSize, err := nm.indexFile.Seek(0, 2); err != nil {
-			return fmt.Errorf("cannot seek end of indexfile %s: %v",
-				nm.indexFile.Name(), err)
-		} else {
-			nm.indexFileOffset = fileSize
-		}
-	}
-	written, err := nm.indexFile.WriteAt(bytes, nm.indexFileOffset)
-	if err == nil {
-		nm.indexFileOffset += int64(written)
+	if _, err := nm.indexFile.Seek(0, 2); err != nil {
+		return fmt.Errorf("cannot seek end of indexfile %s: %v",
+			nm.indexFile.Name(), err)
 	}
+	_, err := nm.indexFile.Write(bytes)
 	return err
 }