Extra metadata maintained internally in `xl.meta` for a transitioned object

```
...
        "MetaSys": {
          "x-minio-internal-transition-status": "Y29tcGxldGU=",
          "x-minio-internal-transition-tier": "R0NTVElFUjE=",

}

func (dui DataUsageInfo) tierMetrics() (metrics []MetricV2) {
	if dui.TierStats == nil {
		return nil
	}
	// e.g minio_cluster_ilm_transitioned_bytes{tier="S3TIER-1"}=136314880
	//     minio_cluster_ilm_transitioned_objects{tier="S3TIER-1"}=1
	//     minio_cluster_ilm_transitioned_versions{tier="S3TIER-1"}=3
	for tier, st := range dui.TierStats.Tiers {
		metrics = append(metrics, MetricV2{

	}
	return opts
}

// SetTransitionState sets ILM transition related information from given info.
func (os *objSweeper) SetTransitionState(info TransitionedObject) {
	os.TransitionTier = info.Tier
	os.TransitionStatus = info.Status
	os.RemoteObject = info.Name
	os.TransitionVersionID = info.VersionID
}

// shouldRemoveRemoteObject determines if a transitioned object should be

--restore-request Days=3
```

### 4.1 Monitoring transition events

`s3:ObjectTransition:Complete` and `s3:ObjectTransition:Failed` events can be used to monitor transition events between the source cluster and transition tier. To watch lifecycle events, you can enable bucket notification on the source bucket with `mc event add`  and specify `--event ilm` flag.

Note that transition event notification is a MinIO extension.

## Explore Further

			expectedErr: errInvalidStorageClass,
		},
		{
			// no transition rule

package ilm

import "github.com/minio/minio/internal/config"

const (
	transitionWorkers = "transition_workers"
	expirationWorkers = "expiration_workers"
	// EnvILMTransitionWorkers env variable to configure number of transition workers
	EnvILMTransitionWorkers = "MINIO_ILM_TRANSITION_WORKERS"
	// EnvILMExpirationWorkers env variable to configure number of expiration workers

	Filter              Filter              `xml:"Filter,omitempty"`
	Prefix              Prefix              `xml:"Prefix,omitempty"`
	Expiration          Expiration          `xml:"Expiration,omitempty"`
	Transition          Transition          `xml:"Transition,omitempty"`
	DelMarkerExpiration DelMarkerExpiration `xml:"DelMarkerExpiration,omitempty"`

			Optional:    true,
			Type:        "number",
		},
		config.HelpKV{
			Key:         apiTransitionWorkers,
			Description: `set the number of transition workers` + defaultHelpPostfix(apiTransitionWorkers),
			Optional:    true,
			Type:        "number",
		},
		config.HelpKV{
			Key:         apiStaleUploadsExpiry,

	if j.Type == DeleteType {
		return j.DeleteMarker.FreeVersion()
	}
	return false
}

// AddFreeVersion adds a free-version if needed for fi.VersionID version.
// Free-version will be added if fi.VersionID has transitioned.
func (x *xlMetaV2) AddFreeVersion(fi FileInfo) error {
	var uv uuid.UUID
	var err error
	switch fi.VersionID {
	case "", nullVersionID:
	default:
		uv, err = uuid.Parse(fi.VersionID)
		if err != nil {

func (t *Transition) UnmarshalXML(d *xml.Decoder, startElement xml.StartElement) error {
	type transitionWrapper Transition
	var trw transitionWrapper
	err := d.DecodeElement(&trw, &startElement)
	if err != nil {
		return err
	}
	*t = Transition(trw)
	t.set = true
	return nil
}

// Validate - validates the "Transition" element
func (t Transition) Validate() error {
	if !t.set {