Use O_DIRECT while writing to disk (#7479)

- Use O_DIRECT while writing to disk
- Remove MINIO_DRIVE_SYNC option

pkg/disk/directio_unsupported.go

@@ -0,0 +1,35 @@
+// +build !linux,!netbsd,!freebsd,!darwin
+
+/*
+ * Minio Cloud Storage, (C) 2019 Minio, Inc.
+ *
+ * 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.
+ */
+
+package disk
+
+import (
+	"os"
+)
+
+// OpenBSD and Windows not supported.
+// On OpenBSD O_DIRECT is not supported
+// On Windows there is no documentation on disabling O_DIRECT
+
+func OpenFileDirectIO(filePath string, flag int, perm os.FileMode) (*os.File, error) {
+	return os.OpenFile(filePath, flag, perm)
+}
+
+func DisableDirectIO(f *os.File) error {
+	return nil
+}