volume: fail fast if idx files are missing

fix https://github.com/chrislusf/seaweedfs/issues/1796

weed/storage/volume_checking.go

@@ -2,6 +2,7 @@ package storage
 
 import (
 	"fmt"
+	"github.com/chrislusf/seaweedfs/weed/storage/super_block"
 	"io"
 	"os"
 
@@ -148,3 +149,18 @@ func verifyDeletedNeedleIntegrity(datFile backend.BackendStorageFile, v needle.V
 	}
 	return n.AppendAtNs, err
 }
+
+func (v *Volume) checkIdxFile() error {
+	datFileSize, _, err := v.DataBackend.GetStat()
+	if err != nil {
+		return fmt.Errorf("get stat %s: %v", v.FileName(".dat"), err)
+	}
+	if datFileSize <= super_block.SuperBlockSize {
+		return nil
+	}
+	indexFileName := v.FileName(".idx")
+	if util.FileExists(indexFileName) {
+		return nil
+	}
+	return fmt.Errorf("idx file %s does not exists", indexFileName)
+}

weed/storage/volume_loading.go

@@ -96,6 +96,10 @@ func (v *Volume) load(alsoLoadIndex bool, createDatIfMissing bool, needleMapKind
 				v.dirIdx = v.dir
 			}
 		}
+		// check volume idx files
+		if err := v.checkIdxFile(); err != nil {
+			glog.Fatalf("check volume idx file %s: %v", v.FileName(".idx"), err)
+		}
 		var indexFile *os.File
 		if v.noWriteOrDelete {
 			glog.V(0).Infoln("open to read file", v.FileName(".idx"))