Re: backup and online reso logs question

You don't backup the online redo logs for a couple of simple reasons: firstly, there's no need. You already have backups of them in the form of archived redo logs. If you're backing the archives up, you have all the protection you need.

Second, one online redo log is unbackupable (if that's a word!). The current redo log has not been archived. And taking your own copy of it is pointless. Worse, it's dangerous. It's pointless because the second you have a copy of it, the original changes (users do new transactions which get written to the current log). If you ever restore the backed up version, those new transactions will be lost.

Even worse, the backed up copy will probably be corrupt as anything, because you simply can't copy any database file hot without the copy's contents being an internal mess -not unless Oracle has provided some mechanism to deal with the mess. The 'alter tablespace ... begin backup' command allows hot copies of datafiles to be meaningful. To hot copy the controlfile, you have to use the special command 'alter database backup controlfile to ...' -and again, the special command ensures the copy is internally consistent and useable. For redo logs, we have what command? Er... none. There isn't one, and therefore hot copies, if they are taken, are simply internally all over the place and unuseable.

Remember, only one online redo log is really and truly 'hot' at any one point: the current one. It's the real weak spot. It hasn't been archived, and cannot (ie, should not) be backed up. So lose it, and yes, you will lose transactions. However, that's why they invented the multiplexing of online redo logs... have multiple identical copies ("members" in Oracle-speak) of the same log on different disks, and you can lose one copy without a problem. That's the only way to protect the current redo log, and that's the only answer to your specific question about "how to get around the online redo logs not being backed up".

Regards
HJR "michael.cooke" <michael.cooke_at_tinyworld.co.uk> wrote in message news:3ccb28e1_1_at_mk-nntp-1.news.uk.worldonline.com...
> Oracle 7.3.3 NT4sp6a (Veritas backup exec 8.6)
> currently generating a hot backup nightly
> using alter tablespace ...... begin backup for all tablespaces at the same
> time
> running NTbackup to xcopy all datafiles, controlfile, online redolog files
> etc to another PC. alter tablespace ...... end backup, logswitch backup
> control to trace etc the backup copy is then copied to tape along with the
> archived redo logs.
> I then load the content of the tape to a sandalone test server open the
> database after using the recover database option and am able to use it for
> test purposes in the knowledge that I have a fully recoverable backup.
> I am going over to a new server soon and will be using veritas backup exec
> 8.6 with the oracle agent. I have tested the backup process using this
> option and notice it does not backup the online redo logs or controlfile
> (creates a copies a backup). To be able to carryout a full recovery (if
you
> lose the server completely) you need the online logfiles as well as all
the
> others else you cannot open the db. does anyone out there use veritas to
> create hot backups and have they had any problems recovering a full dbase
as
> I will still need to be able to restory onto my test server? how did you
> get around the online redologs not being backed up?
>
> sorry its a bit like war & peace and hope someone has the patients to read
> an answer it.
>
> regds
> Mick
>
>
Received on Sat Apr 27 2002 - 19:08:56 CDT