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rman backup file names in Flash recovery area in OMF format – how can a new oracle dba understand this format?




your database is using a flash recovery area and your rman backups are present in that flash recovery area. when you go into that directory you see some strange names and you cant distinguish which file is a spfile backup or controlfile backup or datafile backup. This is because those files are in OMF format. OMF stands for oracle managed files.since oracle manages the flash recovery area internally it uses the OMF format.

Below article explains the naming format of the backupfiles present in the flash recovery area.This can be a very handy reference for the new oracle dba.

Subject: Format Of Backup Pieces Manged In FRA
  Doc ID: 566680.1 Type: HOWTO
  Modified Date : 31-MAY-2008 Status: PUBLISHED

In this Document
  Goal
  Solution


Applies to:

Oracle Server – Enterprise Edition – Version: 10.2.0.3
Information in this document applies to any platform.

Goal

To understand the naming convention of backupset backup file names when FRA (Flash Recovery Area) is used .

Solution

The FRA is an oracle managed space which can be used to place the disk backups which are taken using RMAN.Since the files which are placed in this location are maintained by oracle itself  the file names are maintained in the OMF (Oracle Managed Files) format.

A backup piece which is placed in the FRA has the following format e.g.,

o1_mf_nnsnf_TAG20080502T081406_41pd0s8h_.bkp

For clarity we can divide the file name into 5 sections .

o1 –> section 1
mf –> section 2
nnsnf –> section 3
TAG20080502T081406 –> Section 4
41pd0s8h –> section 5.

The first two sections explains that it is an oracle managed file . i.e., o1_mf

The third   section explains the type of the files in the backup piece and it contains the combination of the notations a , c , s , d, n & f.

Usually the below mentioned notations are used to represent a particular type of the file

a represents archivelog and it takes the first position.
c represents controlfile and it takes the second position.
s represents spfile and it takes the third position.
d represents datafile and it represents the fourth position.
f  represents the incremental level of the piece.(0 , 1 ,2 ,3 ,4) and it takes the fifth position.
n represents a null or nothing.

Now taking our example of  "nnsnf"  –>  Since only the notation "s" is present we can conclude that this has the backup of the spfile in it because all the bits other than the one for the spfile is set to nothing and F represents that it is not a incremental piece.

Taking an another example of  "ncsnf" –> Here we can see that both the 2nd and 3rd bit is set.i.e., both c and s is set which means that this backup piece consists of the control file and the spfile in it.

Taking an another example of  "nnnd0" –. Here the 4th and 5th bit is set.Which means that this piece consists of the level 0 datafile backup in it and all the other bits are set to n (nothing).

The fourth section of the filename represents the timestamp when the backup is performed.

The fifth section is a unique key generated by oracle by default and it is used to maintain the uniqueness with in the same type of backup pieces.

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