diff --git a/weed/storage/volume_info.go b/weed/storage/volume_info.go
index e993c9c58..5608d596c 100644
--- a/weed/storage/volume_info.go
+++ b/weed/storage/volume_info.go
@@ -10,23 +10,29 @@ import (
 	"github.com/seaweedfs/seaweedfs/weed/storage/super_block"
 )
 
+// Held for every volume replica, so the fields are grouped by size rather than
+// by meaning: interleaved, each one-byte field rounds up to a whole word.
 type VolumeInfo struct {
-	Id                needle.VolumeId
-	Size              uint64
-	ReplicaPlacement  *super_block.ReplicaPlacement
-	Ttl               *needle.TTL
-	DiskType          string
-	DiskId            uint32
 	Collection        string
-	Version           needle.Version
-	FileCount         int
-	DeleteCount       int
-	DeletedByteCount  uint64
-	ReadOnly          bool
-	CompactRevision   uint32
-	ModifiedAtSecond  int64
+	DiskType          string
 	RemoteStorageName string
 	RemoteStorageKey  string
+
+	ReplicaPlacement *super_block.ReplicaPlacement
+	Ttl              *needle.TTL
+
+	Size             uint64
+	FileCount        int
+	DeleteCount      int
+	DeletedByteCount uint64
+	ModifiedAtSecond int64
+
+	Id              needle.VolumeId
+	DiskId          uint32
+	CompactRevision uint32
+
+	Version  needle.Version
+	ReadOnly bool
 }
 
 func NewVolumeInfo(m *master_pb.VolumeInformationMessage) (vi VolumeInfo, err error) {
diff --git a/weed/storage/volume_info_layout_test.go b/weed/storage/volume_info_layout_test.go
new file mode 100644
index 000000000..6d862b96d
--- /dev/null
+++ b/weed/storage/volume_info_layout_test.go
@@ -0,0 +1,34 @@
+package storage
+
+import (
+	"reflect"
+	"testing"
+	"unsafe"
+)
+
+// Nothing else in the package would notice if someone grouped the fields by
+// meaning again, and the padding is multiplied by every volume a master holds.
+func TestVolumeInfoHasNoInteriorPadding(t *testing.T) {
+	typ := reflect.TypeOf(VolumeInfo{})
+
+	var used, interior uintptr
+	prevEnd := uintptr(0)
+	for i := 0; i < typ.NumField(); i++ {
+		f := typ.Field(i)
+		if gap := f.Offset - prevEnd; gap > 0 {
+			t.Errorf("%d bytes of padding before %s, at offset %d: order the fields by size so they pack",
+				gap, f.Name, prevEnd)
+			interior += gap
+		}
+		used += f.Type.Size()
+		prevEnd = f.Offset + f.Type.Size()
+	}
+
+	size := unsafe.Sizeof(VolumeInfo{})
+	if tail := size - prevEnd; tail > 7 {
+		t.Errorf("%d bytes of padding at the end, more than alignment requires", tail)
+	}
+	if interior == 0 {
+		t.Logf("%d bytes of fields in a %d byte struct", used, size)
+	}
+}