Re: does FRA is really needed ?

Flash Recovery Area is not necessary. I've implemented dozens of DG configs without.

I do not understand what you mean with 'failover switch from primary to standby and back'. Where in normal life careful wording is important, in HA environments this is particularly the case. Misunderstandings when in the act of a recovery, failover or switchover can render the complete system unusable. I've witnessed that happening. So, make yourself familiar with the terminology as Oracle uses around this topic. I must admit that that terminolgy isn't as stable as one would like, especially when terms get scrambled by dbms_moot (Marketing Obfuscation for Oracle Toolkit, licensed with the advanced Oracle Text option).

Either you switch over (and then primary and standby both are available and can 'see' each other) or you fail over (the primary went unavailable and you make a standby your new primary). The first operation is reversable, the second isn't, unless you have an FRA under 10gR2.

The way to 'recover' from a failover w/o an FRA in place is to do an instantiate from your new primary to the former primary, to make it you standby. This means you have to copy the full database, or restore/recover it from an RMAN or HOT backup, and add a standby control file. When bandwidth is limited (say less than 10 Mb), I've succesfully sped up the re-instantiate process significantly by using hot backup in combination with rsync in stead of scp. With rsync only changed blocks are transferred. Mind that you still have to put tablespaces in backup mode. When higher bandwidths (100 Mb and up) are available ther is not much to gain: reading files at both ends, checksumming blocks and exchanging the checksums take resources as well, and it becomes faster to burst copy the entire datafile than doing the block compare hassle. I haven't been able to measure speeds between 10 and 100 Mb, but it will largely depend on the speed of your storage system and the amount of changes to the datafiles after the failover whether rsync or scp will be faster.

Best regards,

Carel-Jan Engel

===
If you think education is expensive, try ignorance. (Derek Bok) ===

On Sun, 2007-12-16 at 12:53 +0100, Grzegorz Goryszewski wrote:

> Hi,
>
> can You please clarify one thing for me.
> I'm wonder if FRA is really neccessary for Data Guard solution ?
> I'm preparing for DG configuration with physical standby, do I need FRA for
> failover switch from primary to standby and back ?
> Oracle 10.2.0.2 .
> Regards.
> Grzegorz
>
>
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