Re: RAID vs Redo log mirroring

The whole reason why Oracle says to mirror redo logs is get them on their own physical drives. Why, you might ask? Because if the next redo log to be written is not available, your DATABASE COMES TO A SCREECHING HALT!

Raid 5 does guard against lost data in the event of a device failure, but in Oracle's case your database is dead until you pop in another drive.

Therefore, unless you have another Raid 5 array to place the mirrored redo logs on, mirroring redo logs on the same array does no good whatsoever.

I hope this helps!

Stuart Cowen
Paladin Consulting - Dallas

In article <01bd993e$3cf8c3c0$4baa3ec1_at_regan.bton.ac.uk>,   "Robin Bishop" <rmb8_at_bton.ac.uk> wrote:
>
> Given that the primary (only?) reason for mirrored redo logs is to guard
> against media failure, can anyone suggest whether it is still necessary on
> a system running RAID level 5?
>
> Is there a circumstance whereby mirroring would provide some security that
> RAID would not? My feeling is that relying on RAID should be sufficient but
> I'm pretty new to this game. All the DBA stuff I've read suggests that
> mirroring redo logs is very nearly essential but none of it mentions the
> impact of RAID systems on this view.
>
> Thanks in advance for your opinions.
> --
> Robin Bishop
> University of Brighton Computer Centre
> Brighton, England
>

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