Re: RAID vs Redo log mirroring

I think you're asking about "how many members per group" -- multiple copies of the same file, rather than "how many groups" (the answer to that second question is always "2+" as Sisk writes). Here's some of what's happening at my shop -- maybe it helps:

We're running RAID5 with two sets of redo: one on the RAID array, and the other out in a regular disk. This was inherited. Now we're setting up a new computer, and we've decided that we'd rather have two sets of redo BOTH on the RAID array. This is unnecessary but...

The extras are to guard against human error -- after all this time I still sometimes reach for the redo logs meaning to mv the archived logs for disk space. One day I actually might kill redo! So I'd rather have two, since I prefer to copy the redo log files every now and then, vs. killing my only redos and having nothing. And since I'm not the only one who has rights to mv, I'd like that extra copy. For now.

Also, we've been hashing over whether RAID is slower per Oracle performance canon. After much reading and discussion, we concluded that the newer cache controllers eliminate mostly all the performance difference between RAID and nonRAID. In any event, we aren't showing disk problems right now, and we can always move redo, temp, rollbacks around later if we want to.

In article <ViZh1.114$cn.4749616_at_news.ipass.net>,   "David Sisk" <davesisk_at_ipass.net> wrote:
>
> Hi:
>
> I don't believe the Oracle instance will allow you to have less than two
> redo log members. This is for your own good. Redo logs, even if on RAID5,
> RAID1, or RAID6 can become "stale" (that is, have a write error). The
> Oracle instance knows when this happens, and will simply use the redo log
> from the other member for archiving or recovery.
>
> Good luck,
> Dave
>
> Robin Bishop wrote in message
> <01bd993e$3cf8c3c0$4baa3ec1_at_regan.bton.ac.uk>...
> >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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