Metadata can be stored in the key data set in the KDSR format. A 2-byte tag is used to identify a block of metadata. IBM reserves the tags where the high order bit is off. Tags reserved for installation metadata block will have the high order bit on.
| Tag usage | Value or range | Notes |
|---|---|---|
| The data stored in the user data field in the old formats of the CKDS (CKDUDATA), PKDS (PKDUDATA), or TKDS (TKDUDATA). | X'0001' | This metadata block can be added, deleted, and changed using the Key Data Set Metadata Write service. |
| The service or utility that referenced the record the last time the last used reference date was updated. | X'0002' | This metadata block is read only. |
| The date the record was archived. | X'0003' | This metadata block is read only. |
| The date the record was recalled. | X'0004' | This metadata block is read only. |
| Reserved for IBM use. | X'0005' - X'7FFF' | These metadata blocks are read only. |
| Available for installation use. | X'8000' - X'FFFF' | Metadata blocks can be added, deleted, and changed using the Key Data Set Metadata Write service. |