taping oracle online redo logs?

[Michael Schulte zur Sur]

Hi all,

we are about to get a high availability HP system with lots of safety built in and I am asked, whether we want to tape the online redologs (besides archive logs).
Is there any virtue to it? I can remember vaguely Oracle saying, this procedure is not supported.

Any oppinion would be appreciated.

Michael

[Graham Cameron_1]

Not sure what you mean by "taping" ??

BTW the online redo logs are the same as the archive logs.

In any database, archiving or not, the online redo logs get cyclically reused.
In an archivelog database, they get copied to the archive log area also.
So provided you are capturing the archive logs, to tape or wherever, there is no point in also copying the redo logs.

On the other hand, it is good practise to use redo log groups, with >1 file per group split across disks, so that if 1 disk fails you still have the good redo log on the other disk. This capability is built into Oracle.

Hope this helps.

-- Graham

[Steven E. Protter]

You can do hot backups of your database using rman. Those hot backups can go directly to disk and then tape via the tar cv /backup_dir command. That will default to tape.

What you really need to do for reliability is mirror the redo logs to different physical disks. Also spread your control files to multiple physical disks as well.

The bottom line here is perfect reliability is nearly impossible. You can guard against common issues, but if your system board quits or your scsi subsystem fries, you're offline. Unless you use SErvice Guard.

SEP

[Michael Schulte zur Sur]

Hi,

there will be more than one member for each redo log group. Depending on how frequent the logs switch, it might be useful to make frequent snapshots of them in between. This is my concern. Is this useful at all? Can Oracle use them in a case of a recovery?

thanks for your time,

Michael.

[Yogeeraj_1]

hi,

with the hot backup you don't need the online redo log files!

hope this helps!
regards
yogeeraj

[Michael Schulte zur Sur]

But dumping the whole database is very likely to be much more data. I just want to minimize the data lost between log switches.

greetings,

Michael

[Stan_17]

Hi Michael,

It depends on how you plan to take backups. i meant coldbackup (offline) or hotbackups (online) of the database.

If coldbackups then i'd say backup everything including redologs and archivelogs.

If hotbackups, then i'd say backup everything except online redologs, since these backups are done online they are always inconsistent. besides there is no begin backup and end backup commands for redologs like we have for datafiles. so you can't have a consistent copy of redolog unless the db is shutdown. if they are inconsistent, then its of no use for recovery. so why backup ?

Nowadays, almost all production systems run with some sort of RAID so the disk failures are very seldom. In fact multiplexing and mirroring online redologs on to different disks will almost remove the single point of failure. so you always have access to redologs to recover the database.

-
hth,
Stan

[Michael Schulte zur Sur]

Hi Stan,

backup is a completely different story. Of course we will have a backup too and since this machine is going to have some sort of emc and several access paths, that is not a concern. What I want to know is. Can Oracle use a redolog, saved by unix command, while it is open, or not, when I have to recover.

greetings,

Michael

[Stan_17]

"Can Oracle use a redolog, saved by unix command, while it is open, or not, when I have to recover."

As i said earlier, to backup (in your terms saved by unix command ) redologs totally depends on how you backup the database. ie, are you saving the files when the database is down or the db is online.

if offline, then yes backup redologs, they are consistent, hence useful for recovery, if online, then don't backup, they are inconsistent so no use for recovery. make sense!

[SteveKirby]

"Is there any virtue to writing redologs to tape?"
The short answer is not in my opinion.

The long answer is that all transactions are written to the redo log .. when the redo log gets full (or you force a switch) then the log gets written to disk as a Archive log.

Technically you could write all transactions that hit the redo log for real-time recovery (vs. 5 min - 1 day depending on how often the ARchivelogs are written) directly to tape... I have never done it, but the theory is sound.