Re: Multiplexing redologs - is there still need for it?

On 12 Mar 2004 08:15:57 -0800, pagesflames_at_usa.net (Dusan Bolek) wrote:

>Today, I have run into an interesting discussion. The question was if
>there is a need for multiplexing redologs by database (as suggested in
>Admin manual) if this data are already mirrored (using RAID, disk
>arrays mirrors, Data Guard, SRDF etc.).
>I'm somehow paranoid, so I proposed tu use multiplexing, while other
>party stated that these bytes are already stored on eight different
>locations. That's sounds sensible, but I remember the issue a long
>time ago in a company far far away, where one of two multiplexed
>control files got corrupted and (of course) copies on both mirrored
>disc vere identical (means corrupted), second redo log on different
>volume group was OK. So in this case we would been doomed if these
>redologs weren't multiplexed.
>What's the opinion on this topic in the newsgroups? Preferably with
>some technical explanation.

Mirrored drive: Oracle will queue 1 write request. If that write request fails, your database is toast.
Multiplexed redologs: Oracle will queue 2 write requests. As long you don't put the members on 1 single drive, it is very unlikely *both* requests fail.

--
Sybrand Bakker, Senior Oracle DBA