Re: Redo logs. Please explain.

In article <4ahp8q$rd5_at_ixnews3.ix.netcom.com>, chuckh_at_ix.netcom.com says...
>
>I'm trying to learn the DBA job by reading the Oracle manuals. Can
>someone please explain how the redo log files relate to one another?
>If I create a database with the following redo log groups....
>
>CREATE DATABASE "tardis"
>...
>LOGFILE GROUP 1 ('a.log', 'b.log') size 1m,
>LOGFILE GROUP 2 ('c.log', 'd.log') size 1m;
>
>Which files are mirrors of which? And which are used in the circular
>fashion as described in the concepts manual?
>
>Do 'a' and 'c' mirror each other, or do 'a' and 'b'? I need to know
>so I know which drives to place the files on to protect against media
>failure.
>
>The manuals seem to cover everything about redo logs except this.
>--

• the mirror of 'a' is 'b'
• 'a' and 'b' are written to simultaneously
• Group1 (a,b) and Group2 (c,d) are written to in circular fashion
• in Archivelog-Mode, the archive of Group1 is build using blocks from both 'a' and 'b' if both members are valid

[Oracle7 Server Concepts Manual p. 23-12] "The corresponding online redo log files are called _groups_.  Each online redo log file in a group is called a _member_.  Notice that all members of a group are concurrently active ....  If a mirrored online redo log is used, groups of online redo log files  can be created, with the requirement that each menmber in a group is the  exact same size. ..."

Hope this helps

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