//   - on xl.meta (array of versions) on disk to check for version disparity
//   - on rewrite dataDir on disk that must be additionally purged
//     only after as a 2-phase call, allowing the older dataDir to
//     hang-around in-case we need some form of recovery.
type RenameDataResp struct {
	Sign       []byte
	OldDataDir string // contains '<uuid>', it is designed to be passed as value to Delete(bucket, pathJoin(object, dataDir))
}