Topic: Database Administration >> rman backup does not work properly
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| Title: rman backup does not work properly |
| sivakumar |
Posted: Jun 26, 2009 11:51:00 PM |
Total Post: 18
Joined: Jan, 2009
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in our production database, we have 5 tablespace, in that 2 tablespace are stored in SAN disk, rest of the three T.S are stored in local server, the problem is when i take backup of entire DB using RMAN the T.S stored in SAN disk RMAN takes used and unused blocks from the T.S in SAN disk.
but the rest of 3 T.S (which stored in local server) RMAN performs backups of used blocks only.
i would appreciate, if somebody could help me in this regard.
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 Mahendra Rathod |
| Posted: Jun 27, 2009 02:30:41 AM |  |
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Total Post: 135
Joined: May, 2008
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HI
RMAN definitely doesn't identify Table HWMs -- it doesn't know logical
structures such as Tables and Segments and Tablespaces [although it
can assist you in Tablespace Recovery when it reads the Data Dictionary].
RMAN knows physical structures such as DataFiles, RedoLog Files and
ControlFiles. When backing up a DataFile, RMAN would ignore
__unused__ blocks --- blocks that have never been used.
Now, the part where I don't agree with Mladen is about reading the
bitmap information from the tablespace header. RMAN can backup
DataFiles belonging to Dictionary Managed Tablespaces without
Automatic Segment Space Management. In such cases there is no
bitmap in the tablespace header to read from.
When Oracle creates a DataFile it initializes the file with NULLs. When
a block is used [written to as a Table Row-Block or an Index Leaf-Block],
the block has to be formatted before it is written-to. Once it is formatted
[the formatting is the block header, table column names, and possibly
the initrans area and pctfree area], the block will always remain "used"
even if all the rows in it are deleted.
Thus, when RMAN goes through a DataFile it examines each block and
ignores unused blocks which have not been formatted.
Such unused or empty blocks may be within an Extent or unallocated to any extent !
------
What it doesn't write are the blocks that are not allocated to any
extent. RMAN doesn't go into the logical structures, like tables and
indexes,
it looks into the tablespace header and reads the information from the
bitmap information there. It cannot go into tables/indexes because it
should also work when the database is only mounted and not opened, which
genrally means that data dictionary is not accessible. Empty blocks
are blocks that don't have any rows in them but are allocated to an
extent. New or unallocated blocks are blocks that have been initialized
when the datafile was allocated to the tablespace but have not been assigned
to any object (table, index, materialized view, cluster, partition or alike)
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| sivakumar |
| Posted: Jun 27, 2009 02:47:17 AM | |
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Total Post: 18
Joined: Jan, 2009
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sorry, i m not getting what ur trying to say,
actually this are the T.S in my pro.DB.
TS# NAME
---- ----------
0 SYSTEM -------------> stored in local disk
1 UNDOTBS1 -------------> local disk
2 SYSAUX -------------> local disk
3 TEMP -------------> local disk
6 EXAMPLE -------------> local disk
7 NIIL_DATA -------------> SAN disk
8 NIIL_NDX -------------> SAN disk
TS# 7 & 8 has size in 25G,10G respectively, while performing RMAN backup it takes backup of entire 25G and 10G (actually these two T.S totally contains 5G of data only), so my RMAN fulldb backup becomes 36.2G i don't know why it takes entire datafile backup (both used and unused blocks) of files in SAN disk?
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