Tuesday 27 June 2017

Oracle RMAN (Recovery Manager) Concepts

What is the difference between obsolete and expired Backup in RMAN?

Obsolete Backup: Backup pieces or backup sets which are not needed for recovery.
We can use the REPORT OBSOLETE command to list the obsolete backups and DELETE OBSOLETE command to delete the obsolete backup.

Expired Backup:When the CROSSCHECK command is used to determine whether backups recorded in the repository still exist on disk or tape, if RMAN cannot locate the backups, then it updates their records in the RMAN repository to EXPIRED status.We can then use the DELETE EXPIRED command to remove records of expired backups from the RMAN repository.

Oracle DBA Concepts: Background Processes in Oracle ASM (Automatic storage Management)

The following background processes are an integral part of Automatic Storage Management:

ARBn performs the actual rebalance data extent movements in an Automatic Storage Management instance. There can be many of these processes running at a time, named ARB0, ARB1, and so on.

ASMB runs in a database instance that is using an ASM disk group. ASMB communicates with the ASM instance, managing storage and providing statistics. ASMB can also run in the ASM instance. ASMB runs in ASM instances when the ASMCMD cp command runs or when the database instance first starts if the SPFILE is stored in ASM.

GMON maintains disk membership in ASM disk groups.

MARK marks ASM allocation units as stale following a missed write to an offline disk. This essentially tracks which extents require resync for offline disks.

RBAL runs in both database and ASM instances. In the database instance, it does a global open of ASM disks. In an ASM instance, it also coordinates rebalance activity for disk groups.