Re: mirroring vs. multiplexing

hastenthunder wrote:
> Hello,
>
> Do I still need to multiplex control files and online redo files since our
> Linux box is being mirrored?
>
> Oracle recommendation says yes, but I do not really understand the
> reasoning. Why would multiplexing the same file to different disks provide
> "more" fault-tolerance than disk mirroring?

Because mirroring protects you from hardware failure. It does nothing to protect you from software or user stuff-ups -which is what multiplexing does.

If I rm *.log, you will lose all your redo logs (assuming just for a moment that you were unfortunate enough to give them such a daft extension) from one drive -and guess what will happen on the mirror?

By multiplexing, you force Oracle to do two (or more) writes to things such as redo logs and control files. If CKPT or LGWR decides to throw a bit of a software wobbly when performing one of those writes, the hardware mirror will faithfully replicate the corruption -but the process has to repeat the write on another file, and the chances of it suffering exactly the same glitch in exactly the same place on the second file are quite small.

The two are *complements*, therefore, not mutually exclusive. Do both. For a quiet, safe and comfortable life, do both.

Regards
HJR Received on Wed Dec 22 2004 - 19:29:20 CST