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ram backup [message #74679]

Thu, 03 February 2005 05:37

Natraj
Messages: 53
Registered: March 2003

Member

HI,
while doing RMAN backup ofdatabase(hot RMAN backup).which goes to tape. does RMAN do any compression?if our database size is say 100 GB after we do RMAN backup to a tape using veritas net backup wat is the size of the backup? is this reduced or the same?
Thanks Natraj

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Re: ram backup [message #74681 is a reply to message #74679]

Thu, 03 February 2005 06:38

Mahesh Rajendran
Messages: 10707
Registered: March 2002
Location: oracleDocoVille

Senior Member
Account Moderator

in 9i RMAN doesnt do any compression by defualt to disk.
You have to use external methods after the backup is done.
In case of backup to tape, the MML is responsible for the compression.
RMAN will NOT see these compressed backupset unless it is uncompressed.

But with 10g RMAN uses a binary compression algorithm.
Syntax would be

rman> backup AS backupset database format '/.../.../yourformat';

in 10g catalog, the view v$backup_piece.compressed will show the nature of backup piece that was backed up.

There are known bugs (the value of compressed size is erranously displayed by RMAN LIST command).
workaround is to check views ( NOT Using RMAN commands)

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Re: ram backup [message #74682 is a reply to message #74681]

Thu, 03 February 2005 06:49

Natraj
Messages: 53
Registered: March 2003

Member

so in case,if we compress with MML after backup is done.how will the recovery be in case of a crash recovery?,since RMAN will not see these compressed backup sets!!!
thanks Natraj

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Re: ram backup [message #74684 is a reply to message #74682]

Thu, 03 February 2005 08:54

Mahesh Rajendran
Messages: 10707
Registered: March 2002
Location: oracleDocoVille

Senior Member
Account Moderator

May be i did not spread it right.
the compression is good only for diskbackups.
rman dumps to disk
you compress them . backup the compressed ones to tape.

if you are doing a direct tape backup, MML is responsbile for compression. ie.. it is already kinda...compressed.
during recovery again MML is responsible to uncompress it
( it is transparent. You need to do nothing with that).

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Re: ram backup [message #74685 is a reply to message #74684]

Thu, 03 February 2005 13:28

Natraj
Messages: 53
Registered: March 2003

Member

got it. but how will the disaster recovery occur?suppose RMAN dumps to disk. we compress it. the there is a crash.should we uncompress it? if so how? i have not worked on such a situation. i know it is difficult to explain, can u send me some good links on RMAN, on these issues?
Thanks Natraj

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Re: ram backup [message #74686 is a reply to message #74685]

Thu, 03 February 2005 16:58

Mahesh Rajendran
Messages: 10707
Registered: March 2002
Location: oracleDocoVille

Senior Member
Account Moderator

you have to uncompress it to the original location.
>>if so how?
same(or set) of utility which is used to compress it.
You can use anything you want.
BUT TEST everything first.
In few cases, the uncompress have corrupted the backupset files. I never compress my backupsets.
Oracle documentation is only reference i can ever think of.

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