Re: Hot Backup

From: Chuck <chuckh_nospam_at_softhome.net>
Date: Tue, 14 May 2002 13:23:34 -0400
Message-ID: <abrh6p$krd09$1@ID-85580.news.dfncis.de>

Changing a block that has already been backed up. When you restore that file, you corrupt it.

If you try to restore a database that was open and being changed when it was backed up, the datafiles will not all be on the same system change number and you'll leave a mess for yourself to clean up, if it can be cleaned up at all.

Here is what Oracle says about inconsistent backups. SCN stands for "system change number".

Inconsistent Backups

---

An inconsistent backup s a backup in which all read-write datafiles and control files have not been checkpointed with respect to the same SCN. For example, one read-write datafile header may contain an SCN of 100 while others contain an SCN of 95. Oracle cannot open the database until these SCNs are consistent, that is, until all changes recorded in the online redo logs have been made to the datafiles.

If your database must be up and running 24 hours a day, 7 days a week, then you have no choice but to perform inconsistent backups of a whole database. For example, a backup of an offline tablespace in an open database is inconsistent with other tablespaces because portions of the database are being modified and written to disk while the backup of the tablespace is progressing. The datafile headers for the online and offline datafiles may contain inconsistent SCNs. You must run your database in ARCHIVELOG mode to make open backups.

If you run the database in ARCHIVELOG mode, then you can construct a whole database backup using backups of datafiles taken at different times. For example, if your database contains seven tablespaces, and you back up the control file as well as a different tablespace each night, in a week you will back up all tablespaces in the database as well as the control file. You can consider this backup as a whole database backup.

"Laurent Boutet" <laurent.boutet1_at_libertysurf.fr> wrote in message news:abrbgk$5k2$1_at_reader1.imaginet.fr...
> Hi !
> thanks for your answer...
> But I'd like to know the case when such a backup is not reliable, as you
> told me....because, it really seems
> to work...so, when will I have trouble doing this kind of backup ???
>
> Thanks,
> Laurent
>
> "Chuck" <chuckh_nospam_at_softhome.net> a écrit dans le message de news:
> abrbql$khcap$1_at_ID-85580.news.dfncis.de...
> > Backing up by just copying open database files does not produce a
reliable
> > backup. You need to...
> >
> > 1. Ensure database is in archive log mode.
> > 2. You should also turn on automatic archiving. This step is not
necessary
> > but without it you need to manually archive logs whenever they fill.
> > 3. For each tablespace do a: start backup, copy (or ocopy on NT) the
> > datafiles, end backup.
> >
> >
> > "Laurent Boutet" <laurent.boutet1_at_libertysurf.fr> wrote in message
> > news:abr6tj$48j$1_at_reader1.imaginet.fr...
> > > Hi all !
> > > please forgive my french accent...I hope you'll understand me ;-)
> > >
> > > a few weeks ago, I have had to make a software in order to do a backup
> of
> > > Oracle DataBase...
> > > First I began with cold backup which worked very well...I stopped my
> > Oracle
> > > DataBase then
> > > did a backup of all the necessaries files...the restoration of such a
> > backup
> > > worked well too...
> > > But I read that cold backups were not very very good...because of the
> need
> > > to shutdown the database...
> > > So, the hot backup was the solution...my customers could work while I
> was
> > > making my hot backup...
> > > I tried to do hot backups...but I had troubles....difficult to
> > solve....Hot
> > > backup was quite complicated to set...you
> > > know...I had to use the command "begin backup...end backup" to copy
all
> > the
> > > tablespace.... etc.
> > >
> > > And yesterday, someone told me that I just had to copy all the files
of
> my
> > > database (datafiles, control files, redologs files,
> > > archive files etc....) in order to do a hot backup ! Thanks to the
redo
> > > logs...
> > > I was astonished !...but indeed, copy-paste seems to work very well !
> > > I say "seems to work very well" because it seems...but I not 100% sure
> ...
> > > I thought that copy-paste of Oracle database was not
> permitted....because
> > > some backup software (like backup synchoniser for instance I think)
> can't
> > do
> > > copy-paste of oracle Database
> > >
> > > What do you think about this ????
> > > Do you have any suggestion ?
> > >
> > > How do you do you backups ?
> > >
> > > Thanks in advance,
> > > Laurent
> > >
> > >
> >
> >
>
>
Received on Tue May 14 2002 - 12:23:34 CDT