Re: Are offline backups an option, or a neccessity?

Clay Davidson wrote:

> Oracle stores changed data in redo log files.
> These redo log files eventually update your database files.
> You can backup the redo logfiles and have a copy of every change made
> to your database since the LAST BACKUP of the datafiles.
>
> You can backup your datafiles by taking the system offline once a week
> or so and doing a cold backup. Reset your logfiles and start the
> process all over again.
>
> You can backup your datafiles while 'online' but what you are really
> doing is taking the datafile offline and backing it up. Any changes
> made to redo logs and your rollback segments (another subject) will
> need to be stored on disk until your datafile comes back online. Read
> mucho disk space if doing any heavy duty processes (read
> updates,deletes,inserts).
>
> If your database blows chunks at some point (which it will), you will
> need to restore it. If your last cold backup was months ago and you
> actually USE your database, then you will be restoring for several
> days (assuming you are not rotating your tapes, your tapes are good,
> there is something ON your tapes.....).
>
> Sounds like you paid alot of money to buy SAP then you paid probably
> 3-5 times as much for thier consultants and now you dont want to
> listen to them.
>
> Many sites 'MUST HAVE 24x7 AVAILABILITY' when they actually do not.
> Some sites will actually need it. They may lose millions of dollars
> whenever thier system is down. If you cant afford the disk space the
> consultant reccomended, then it is unlikely that you will lose much by
> beiing down for the length of time it takes to do the backup. The
> consultant may realize this and is giving you practical advice.
>
> My practical advice would be that if you do not trust the opinion of
> the person or company that you hired to do the job then you should
> postpone your implementation and replace them.
>
> On Tue, 18 Nov 1997 12:52:11 -0600, tashkop_at_iname.com wrote:
>
> >We are about to implement SAP over Oracle with a 24*7 requirement. I am
> >advised by the basis consultant of the implementation partner that we
> >should be taking the RDBMS offline at least once a week for an offline
> >backup, *or*, we need three times the amount of disk to carry out some
> >kind of complicated rolling type backup. This is in spite of the Oracle
> >RDBMS supporting an online backup mode, which we are advised to carry out
> >nightly.
> >
> >Is it really neccessary to take the system offline regularly to do a
> >backup? Can the online backups alone be relied on for a robust solution?
> >
> >I need to get my head around the issues here as the consultant said 'the
> >RDBMS supports an Online backup no problem' then in the next breath is
> >advising to take the system down regularly, or triple our disk budget.
> >
> >We would rather not do either if we can reliably not do so.
> >
> >

As one of the commentators already said - this issue worth a comment.

If I'm wrong about my following statements - do not hesitate...

1. Tablespaces are taking offline during Hot Backup. Any DML changes during the copying of the tablespace's underlying files are written to the Redo Log Files.
2. To Guarantee 100% of sucessful Hot Backup, these Redo Logs should be backed up as well.
3. Therefore, we're doing Hot Backups - and only hot backups - everyday, doing the following :
   • taking each tablespace offline & backing its files
   • and then :
     • find out current log file
     • alter system switch log file
     • alter database backup control file to 'backup area'
     • copying switched log file to 'backup area'

This way a complete database resotre is possible, rolling forward only archive logs that
were created since the very beginning of the backup untill crash has happened.

Yours,

Muli Koppel Received on Mon Nov 24 1997 - 00:00:00 CST