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Re: Cold backup!?

From: Robert Briley <rbriley_at_cp.net>
Date: Fri, 10 Dec 1999 17:57:18 -0800
Message-ID: <3851AF7E.6812C8B9@cp.net>


There's a lot here that's not being said, and if I am stating the obvious I apologize. First is that most often recovery is for an 'instance failure', i.e. the system hung or crashed for some reason other than that a drive was lost. In this case the most current redolog is the sole source of data recovery. Archive logs and for that matter the other redo logs are only used when there is a recovery from tape backup and that either means somebody really did something dumb, or there was a media problem, i.e. you have lost a drive. I such cases you must restore the database from backups and roll on the Archived redo logs. If the disk that crashed did not take out the redo log you were running before the crash, (and hopefully you are threading it to multiple drives) you should be able to restore up to the time of the crash.

Generally backing-up the redo logs is the mark of a newbie because 1) They are not vulnerable in the way that archive logs are. There is only one copy of a given archive log on your disks while there should be multiple copies of your redo logs.
2) Remember that your old archive logs are uniquely identified, but redo log files are cycled so if you restore old redo logs they will overwrite a more current ones and then there is no way to get back to the point of failure.

For those reasons most people don't tape off their redo logs But be very clear. The redo logs are always important in a restore if you want to get back to the point of failure.

Regards
-R

Yosi wrote:

> Note, however, that when you recover and try to restart, Oracle will need Redo
> Log files to exist, as specified in the control files. If you don't back them
> up, you may be able to create new ones and edit your control file to point to
> them. But you're far better off backing up the online logs with you data and
> control files.
>
> Yosi
>
> Mikel wrote:
>
> > Correct, online redo files are only used in instance recovery, not media
> > recovery, therefore they are not required for a cold backup. To ensure
> > you've captured all the online redo prior to the cold backup (shutting down
> > the db of course before the cold backup), do the following
> >
> > shutdown abort
> > startup restrict
> > alter system switch LOGFILE
> > shutdown normal
> >
> > Mike
> >
> > terry norman <scott_at_tiger9.freeserve.co.uk> wrote in message
> > news:7qsame$8fv$1_at_news6.svr.pol.co.uk...
> > > I'm fairly new to Oracle and I'm very confused about this one.
> > > Somewhere in the literature I am sure I have read that online redo log
> > files
> > > should not be backed up because, and I quote "they add no value to the
> > > recovery process". If we're in a cold backup situation following a
> > shutdown
> > > immediate or shutdown normal is there actually anything in the online redo
> > > files which is needed for recovery?
> > >
> > > Regards,
> > > Terry.
> > >
> > > Sybrand Bakker <postmaster_at_sybrandb.demon.nl> wrote in message
> > > news:936479684.18712.0.pluto.d4ee154e_at_news.demon.nl...
> > > > No, you are not right. You will be missing out the ONLINE redo logfiles,
> > > ie
> > > > the most current files.
> > > > Say you have sequence 1, 2,3,4 archived and 5,6,7,8 online. The
> > > controlfile
> > > > will contain one of the sequence numbers 5,6,7,8.
> > > > So if you have a crash, and you didn't backup the online redo log files,
> > > you
> > > > will be forced to execute incomplete recovery and loose data. The
> > archived
> > > > files do not contain duplicates of the files online, they contain files
> > > that
> > > > have been 'phased out'
> > > >
> > > > Hth,
> > > >
> > > > --
> > > > Sybrand Bakker, Oracle DBA
> > > >
> > > >
> > > > Jack Zhu <jackzhu_at_monmouth.com> wrote in message
> > > > news:37D15108.19DFF36B_at_monmouth.com...
> > > > > Oracle runs on ARCHIVELOG mode.
> > > > >
> > > > > Perform cold backup against this db. Backup files from
> > 'dba_data_files',
> > > > > 'v$controlfile', 'v$logfile', and also backup the archived log files
> > > > > from 'log_arch_dest'.
> > > > >
> > > > > But I think if I do the backup for archived log files(log_arch_dest),
> > > > > it's unnecessary to do the backup for 'v$logfile'. 'cause from the
> > > > > recovery point of view, these backup files(from v$logfile) are
> > useless.
> > > > >
> > > > > Am I right?
> > > > >
> > > > > Thanks a lot!
> > > > >
> > > >
> > > >
> > > >
> > >
> > >
Received on Fri Dec 10 1999 - 19:57:18 CST

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