fix: make sure to avoid calling RenameData() on disconnected disks. (#14094)

Large clusters with multiple sets, or multi-pool setups at times might
fail and report unexpected "file not found" errors. This can become
a problem during startup sequence when some files need to be created
at multiple locations.

- This PR ensures that we nil the erasure writers such that they
  are skipped in RenameData() call.

- RenameData() doesn't need to "Access()" calls for `.minio.sys`
  folders they always exist.

- Make sure PutObject() never returns ObjectNotFound{} for any
  errors, make sure it always returns "WriteQuorum" when renameData()
  fails with ObjectNotFound{}. Return appropriate errors for all
  other cases.

cmd/bitrot.go

@@ -119,8 +119,10 @@ func newBitrotReader(disk StorageAPI, data []byte, bucket string, filePath strin
 // Close all the readers.
 func closeBitrotReaders(rs []io.ReaderAt) {
 	for _, r := range rs {
-		if br, ok := r.(io.Closer); ok {
-			br.Close()
+		if r != nil {
+			if br, ok := r.(io.Closer); ok {
+				br.Close()
+			}
 		}
 	}
 }
@@ -128,8 +130,10 @@ func closeBitrotReaders(rs []io.ReaderAt) {
 // Close all the writers.
 func closeBitrotWriters(ws []io.Writer) {
 	for _, w := range ws {
-		if bw, ok := w.(io.Closer); ok {
-			bw.Close()
+		if w != nil {
+			if bw, ok := w.(io.Closer); ok {
+				bw.Close()
+			}
 		}
 	}
 }