RMAN Duplexed Backup

[KenEwald]

What's the point of an RMAN duplexed backup?

-Ken

[Axr2]

Per documentation :

Duplexing Backups
Prudence suggests making multiple copies of backups to protect against disaster, media damage, or human error.

Can't see anything else.

[KenEwald]

Thanks for your reply.

I read that justification in the manual but it didn't make much sense if I can't fork (duplex) the backup pieces to different media devices (ie: one backup piece to disk and it's duplex to tape).

[marist89]

Originally posted by KenEwald
Thanks for your reply.

I read that justification in the manual but it didn't make much sense if I can't fork (duplex) the backup pieces to different media devices (ie: one backup piece to disk and it's duplex to tape).

This is my problem with the whole thing. Putting two copies of the same data on the same tape/disk is worthless, IMHO.

[julian]

Originally posted by KenEwald
What's the point of an RMAN duplexed backup?

-Ken

You can create duplicates of the backups to different locations. Max 4.

[KenEwald]

Originally posted by julian
You can create duplicates of the backups to different locations. Max 4.

Can one location be DISK and another be SBT_TAPE?

[marist89]

Originally posted by julian
You can create duplicates of the backups to different locations. Max 4.

I would like to see an example of this. I've never been able to get one piece 1 to go to /u01/oraback/xxxxx1 and piece 1's "duplex" to go to /u02/oraback/xxxxxx1.

[julian]

Originally posted by marist89
I would like to see an example of this. I've never been able to get one piece 1 to go to /u01/oraback/xxxxx1 and piece 1's "duplex" to go to /u02/oraback/xxxxxx1.

Not on disk. They will go to the same directory/mount point anyway. And there is not much point of that.

If you are backing up to tape you can configure the media manager and RMAN so that the copies of the pieces are written to separate devices.

See Note 70038.1.

[Axr2]

Originally posted by julian
Not on disk. They will go to the same directory/mount point anyway. And there is not much point of that.

If you are backing up to tape you can configure the media manager and RMAN so that the copies of the pieces are written to separate devices.

See Note 70038.1.

Below in an excerpt from Note 70038.1. Now who in the real world can afford to allocate just one channel to achieve this redundancy?! It is kinda pointless.


Creating the backup

It is desirable to write backups to separate devices in order to achieve redundancy. This is achieved by specifing 'set duplex' to the number of available devices and allocating just one channel.

For example, to create 3 copies of the same database backup into 3 separate devices:
1. Ensure that the LSM server parallelism is set to at least 3.
2. Run the following RMAN script:
run { set duplex=3; allocate channel dup_channel type 'sbt_tape'; backup database; }

[Axr2]

Just re-read the documentation
http://download-west.oracle.com/docs...ckp.htm#455262
Excerpt :

Note that there is little value in creating multiple copies on the same physical media. For DISK channels, specify multiple values in the FORMAT option to direct the multiple copies to different physical disks. For sbt channels, if you use a media manager that supports Version 2 of the SBT API, then the media manager will automatically put each copy onto a separate medium (for example, a separate tape).


----------------

Well, there is NO talk about having to allocate only ONE channel here (unlike the previous Note). Hmm..Apparently the new API will take care of plugging the 2 copies to separate media automatically.

Wonder how to verify this on sbt? I use TSM/TDP. Backups first go to FastT (disk) and something called collocation (tsm background process) copies it to tape later. Also, stuff gets moved around from one tape to another (within the tape library) in the background periodically. So if a certain piece were on tape10 today, it may very well be on tape20 the day after.

I wonder if there's any interface in TSM which tells you which piece currently resides on which tape.