Device manager: clear start of block device after volume creation

Even though we clear data area after device deletion,
let's reduce chances even further that old data remains there
and becomes recognized as file system

pkg/pmem-device-manager/pmd-lvm.go

@@ -105,6 +105,15 @@ func (lvm *pmemLvm) CreateDevice(name string, size uint64, nsmode string) error
 			if _, err := pmemexec.RunCommand("lvcreate", "-L", strSz, "-n", name, vg.name); err != nil {
 				glog.Infof("lvcreate failed with error: %v, trying for next free region", err)
 			} else {
+				// clear start of device to avoid old data being recognized as file system
+				device, err := lvm.GetDevice(name)
+				if err != nil {
+					return err
+				}
+				err = clearDevice(device, false)
+				if err != nil {
+					return err
+				}
 				return nil
 			}
 		}

pkg/pmem-device-manager/pmd-ndctl.go

@@ -64,6 +64,15 @@ func (pmem *pmemNdctl) CreateDevice(name string, size uint64, nsmode string) err
 	}
 	data, _ := ns.MarshalJSON() //nolint: gosec
 	glog.Infof("Namespace created: %s", data)
+	// clear start of device to avoid old data being recognized as file system
+	device, err := pmem.GetDevice(name)
+	if err != nil {
+		return err
+	}
+	err = clearDevice(device, false)
+	if err != nil {
+		return err
+	}
 
 	return nil
 }