Re: RAID vs Redo log mirroring

On 16 Jun 1998 15:48:25 GMT, "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?

Accidental deletion or overwriting of a redo log.

Be advised also that RAID-5 is inherently slow at doing writes which is all that occurs on redo logs (except during recovery). Each logical write requires 4 physical i/os (2 reads and 2 writes). Raid 1 is better for redo logs.

For an OLTP systems I'd recommend RAID 0+1 for for database files over RAID-5 too.
--
Chuck Hamilton
chuckh_at_dvol.com

If at first you don't succeed, sky diving isn't for you. Received on Wed Jun 17 1998 - 09:47:08 CDT