RE: Some Dataguard is good, lots more must be better?(specifically, when do most actual failovers really occur?)

No, I do not confuse. I just was not 100% sure if Oracle can do it because I've never tested it myself.  

The point is I've never used this option is that together with Data Protection one wants High Availability which means that time lag is contradicting this requirement. In numbers if 15 minutes downtime is allowed then recovery must be 15 minutes. I am not sure how to calculate maximum lag allowed as it depends on machine speed and redo size and probably redo contents.    

Brgds,
Laimis N  

From: Carel-Jan Engel [mailto:cjpengel.dbalert_at_xs4all.nl] Sent: 20. september 2006 21:27
To: Laimutis Nedzinskas
Subject: RE: Some Dataguard is good, lots more must be better?(specifically, when do most actual failovers really occur?)

On Wed, 2006-09-20 at 17:07 +0000, Laimutis Nedzinskas wrote:

        Now regarding DG with time lag. Well, it is not a good option for

        maximum data protection(as Oracle defines it.) At least I do not know

        how to protect redo logs in this mode. Which means that for maximum data

        protection you have to have a standby database which is in complete

        sync, i.e. running in maximum protection mode(at least most of the

        time.) BUT I am not sure if file system snapshot technique can achieve

        this either.

Laimutis,
Maybe the delay concept confuses you a little. Maximum protection and Delay actually go together very well.!
Maximum protecion gurantees that redo is written at the standby at the time the commit finishes.
Delay allows you to wait a certain amount of time to apply the redo.

So, all redo IS protected in maximum protection mode, even if a delay is configured. The standby can be in read only mode and still protect your data.

Best regards,

Carel-Jan Engel

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