### Backend format `fs.json`

```go
// ObjectPartInfo Info of each part kept in the multipart metadata
// file after CompleteMultipartUpload() is called.
type ObjectPartInfo struct {
	Number int    `json:"number"`
	Name   string `json:"name"`
	ETag   string `json:"etag"`
	Size   int64  `json:"size"`
}

// A fsMetaV1 represents a metadata header mapping keys to sets of values.
type fsMetaV1 struct {
	Version string `json:"version"`
	Format  string `json:"format"`
	Minio   struct {
		Release string `json:"release"`
	} `json:"minio"`
	// Metadata map for current object `fs.json`.
	Meta  map[string]string `json:"meta,omitempty"`
	Parts []ObjectPartInfo  `json:"parts,omitempty"`
}
```