Backup Piece
A backup piece is a physical file that contain a part of backup targets in a backup operation. In a backup piece, the type of backup targets would be one of the followings.
- Archived Logs
- Data Files
- SPFILE
- Control File
Sometimes, we're unable to know the backup contents from the path and filename of backup pieces. For example:
/backup/4k0vtlt7_8268_1_1
As we can see, the filename is system-generated by a RMAN format variable (formatSpec) %U, we can barely know what targets are backed up in the file from its name.
To exactly list the content of a specific backup piece by RMAN, we can take the following steps:
Get BS Key by the Filename
Usually, one backup set contains one backup piece except that you set MAXPIECESIZE, a limited piece size to split a backup set into several physical pieces.
Now, we can use the filename to get the backup set key (BS Key) by RMAN command list backuppiece.
RMAN> list backuppiece '/backup/4k0vtlt7_8268_1_1';
List of Backup Pieces
BP Key BS Key Pc# Cp# Status Device Type Piece Name
------- ------- --- --- ----------- ----------- ----------
7177 7177 1 1 AVAILABLE DISK /backup/4k0vtlt7_8268_1_1
We see no content here, but we got the BS Key. In this case, it's 7177.
Use BS Key to List Content
Since we have the BS Key, we can use it to look up the content in the backup set by RMAN command list backupset.
Archived Logs Backup Piece
RMAN> list backupset 7177;
List of Backup Sets
===================
BS Key Size Device Type Elapsed Time Completion Time
------- ---------- ----------- ------------ -------------------
7177 676.79M DISK 00:01:12 2022-06-13 01:14:23
BP Key: 7177 Status: AVAILABLE Compressed: YES Tag: TAG20220613T011311
Piece Name: /backup/4k0vtlt7_8268_1_1
List of Archived Logs in backup set 7177
Thrd Seq Low SCN Low Time Next SCN Next Time
---- ------- ------------ ------------------- ------------ ---------
2 8554 226101149872 2022-06-13 00:12:43 226108384945 2022-06-13 01:13:09
As we can see, the backup piece contains only one archived log.
Let's see more backup pieces.
SPFILE Backup Piece
RMAN> list backupset 7178;
List of Backup Sets
===================
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ -------------------
7178 Full 96.00K DISK 00:00:00 2022-06-13 01:14:27
BP Key: 7178 Status: AVAILABLE Compressed: NO Tag: TAG20220613T011427
Piece Name: /backup/4n0vtlvj_8271_1_1
SPFILE Included: Modification time: 2022-06-10 23:42:58
SPFILE db_unique_name: ORCLCDB
By the way, the datetime in RMAN are formatted as what we want.
Control File Backup Piece
RMAN> list backupset 7179;
List of Backup Sets
===================
BS Key Type LV Size Device Type Elapsed Time Completion Time
------- ---- -- ---------- ----------- ------------ -------------------
7179 Full 59.45M DISK 00:00:02 2022-06-13 01:14:29
BP Key: 7179 Status: AVAILABLE Compressed: NO Tag: TAG20220613T011427
Piece Name: /backup/4m0vtlvj_8270_1_1
Control File Included: Ckp SCN: 226108564223 Ckp time: 2022-06-13 01:14:27
Through BS Key, we can see the content of a backup piece. If you still see no content in the backup set, your backup records might be lost regularly.