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Hot Backup::Redolog issue

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mehul_3
Regular Advisor

Hot Backup::Redolog issue


Hi there!
Hot backup(Oracle) is always considered as a inconsistent backup and while restored, archive log must be needed to do a full recovery.
Considering above information, what is a steps taken of backing up of redolog.Is is useful to take backup of online redolog? and what should be a step taken while restoring online backup and what about the redolog restoration?...or create a new one after recovery?..

waiting for reply

Regards,
Mehul



11 REPLIES
Steven E. Protter
Exalted Contributor

Re: Hot Backup::Redolog issue

Couple of broad suggestions:

1) Get OnlineJFS, use lvm snapshots to get a cold backup. What this does is it allows you to briefly down the database, set a snapshot and restart the database. From here all writes to the database are stored in a temporary logical volume. While this is happening a cold OS copy backup or full rman backup can proceed against the database which appears idle to the OS. At the close of backup, the temporary logical volume is shut down and all writes get updated to the original database.

The users notice a berief distruption and you have a cold backup that you can rely on.

2) Use rman hot backups which will not be considered fuzzy and will get you a copy of the database, though you will likely have to apply logs to fully recover.

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renarios
Trusted Contributor

Re: Hot Backup::Redolog issue

Hi Mehul,

I suggest to use RMAN (Oracle Recovery Manager) to backup your databases. For an online backup you need to run in archived log mode, but running in an production, I think you already do.
Using RMAN you get (by Oracle) supported online backups and you can copy databases very easily. Recovering databases (including point in time recoveries) is very handy.

In the meantime don't forget to backup your online redolog files, because they store your latest transactions. A workaround to archive them is issuing the command "archive log all;".

Cheers,

Renarios
Nothing is more successfull as failure
Yogeeraj_1
Honored Contributor

Re: Hot Backup::Redolog issue

Hi mehul!

start using RMAN which obviates most of your queries. Also, with RMAN you will sure that you are backing up all the necessary files, etc

e.g. Backing up the whole database would be as simple as:

allocate channel....
backup database;

See also: http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96566/rcmrecov.htm

and above all, verify that your backup and recovery processes work perfectly.

regards
yogeeraj
No person was ever honoured for what he received. Honour has been the reward for what he gave (clavin coolidge)
Jean-Luc Oudart
Honored Contributor

Re: Hot Backup::Redolog issue

Hi

If you need hot backup you should use RMAN
http://www.oracle.com/technology/deploy/availability/htdocs/RMAN_Overview.htm

Regards
Jean-Luc
fiat lux
mehul_3
Regular Advisor

Re: Hot Backup::Redolog issue

Due to some compelling reason, at present I could not enable hot backup through RMAN.Instead, I implemented a script with traditional hot backup approach and tested/executed suceesfully.It's executes at non-peak hours almost when there is no more transactions(zero).I included a statment "alter system archive log current" in the script and then backed up control file.
will it suffices my problem in case of failure of harddisk and recover the database from archive log after restoring hot backup?

From above scenerio I came to conclusion that there is no need to backed-up of online redolog if almost everthing is archived(i.e archived log file)

Waiting for reply

Rgds,
Mehul
Eric Antunes
Honored Contributor

Re: Hot Backup::Redolog issue

Hi Mehul,

Before going forward, are you sure this is the correct backup strategy for you and your business?

Here are some questions you should ask yourself and your bosses:

- Does your management understand the positive and negative aspects of the backup strategy choosen?

- Have you enough resources (disks, tapes, etc...) for you present backup strategy?

- What are the business and operational requirements (time to recover, mean time between failures, 24*7 operations, database volatility, maximum data loss, etc...)?

Best Regards,

Eric
Each and every day is a good day to learn.
Yogeeraj_1
Honored Contributor

Re: Hot Backup::Redolog issue

hi again,


From above scenerio I came to conclusion that there is no need to backed-up of online redolog if almost everthing is archived(i.e archived log file)


Note that Online redolog do contain data that has not been archived at some moment in time..

So it is not true to say that everything is archived!

It is true however that in practice, we do not backup online redolog files.

Therefore, since you NEVER backup online redo log files, you would NEVER restore them -- so
the online redo logs would be available to be applied during the recovery process (you have them multiplexed over many devices -- a copy should be remaining on your system somewhere, unless you lost *everything* -- but that is
what DR is about, not regular media recovery)

Also, pay special attention to what Eric mentions above...

hope this helps too!

regards
yogeeraj
No person was ever honoured for what he received. Honour has been the reward for what he gave (clavin coolidge)
Mario_66
Valued Contributor

Re: Hot Backup::Redolog issue

Hi Mehul,

there is no need to backup redologs. There is no such thing like redolog restoration. You restore&recover your database, not logs. The best thing you can do about redologs is to mirror them and multiplex them.

As you know, online "current" redolog is opened and held by LGWR and cannot be copied in consistent way.

M.
Patti Johnson
Respected Contributor
Solution

Re: Hot Backup::Redolog issue

Mehul,

You are correct, there is no need to backup the online redo logs. You should however backup the archive redo log files taken during and after your hot backup. As part of the restore you will copy the datafiles (taken while the tablespace was in backup mode "alter tablespace begin backup" ) and roll forward thru all (or part) of the archive redo logs. You then open the database with the resetlogs option and you online redo logs files are created for you.

Patti
Eric Antunes
Honored Contributor

Re: Hot Backup::Redolog issue

One more thing:

When recovering from hot backups, it is HIGHLY RECOMENDED that you COLD backup the database has it is before doing the recovery operation because this is the only way you garantee another try in case the first recovery operation fails!

Best Regards,

Eric
Each and every day is a good day to learn.
Mario_66
Valued Contributor

Re: Hot Backup::Redolog issue

Hi Mehul,

few things come into my minds.

Be carefull with resetlog option. I have seen/heard about many cases where people used this option when it is not neccessary.

And I would highly recommend to read the post from Eric about backup strategy and start looking for answers.

M.