Re: Still looking for RAID answers

"GreyBeard" <Fuzzy.GreyBeard_at_gmail.com> wrote in message news:pan.2005.01.04.20.26.26.849265_at_gmail.com...
> On Tue, 04 Jan 2005 19:19:58 +0000, Randy Harris wrote:
>
> > I know that there has been much discussion of RAID recently in this
> > newsgroup. I hope to get a bit more advice from anyone who has
experience
> > to offer.
> >
> > Several years ago, when I first become involved in Oracle
administration, I
> > read much about the virtues of OFA. OFA proponents, and the Oracle DBA
> > Handbook strongly stated the importance of getting the various Oracle
> > objects onto different physical disk drives. More recently, at the
> > suggestion of several in this newsgroup, I've read about SAME (Stripe
All,
> > Mirror Everything). It seems that the two are rather differing
approaches,
> > though both generally urge the inclusion of as many physical disk drives
as
> > possible. Both make it clear that RAID based on parity (RAID 3 - 5) are
> > undesirable. In simple terms, I suppose, we used to say that striping
was
> > bad, now we say that only parity striping is bad.
> >
> > Because of a recent hardware failure, I am now in a position to
completely
> > reconfigure my StorEdge array on a Sun server, running Solaris 8. I
plan to
> > use 10 drives, keeping the other 2 for hot spares. If I consider OFA
> > recommendations, I would keep all of the drives as RAID 1 (mirrored)
pairs,
> > with each pair, its own filesystem. SAME would have me use RAID 0+1,
> > creating a single slice of all 10 drives.
> >
> > It is still not clear to me, is the SAME architecture approach (RAID
0+1)
> > "better" than OFA (RAID 1), "just as good", or "almost as good" for
Oracle
> > performance?
>
> If, by OFA, you mean Oracle (or Optimal) Flexible Architecture, I do not
> understand where you get OFA = RAID 1 - please tell me where it says
> that.

I didn't mean to suggest that "OFA = RAID 1". Certainly OFA is more than performance optimization by file placement. What I meant, was that given that I have only a single controller and a limited number of disk drives, in a RAID 0+1 configuration, I wil have only a single LUN and be unable to separate control files, and separate logs from datafiles, etc. If I go the "SAME" route, everything ends up on the same file system.

 > Anyway, I don't see a direct conflict of interest if one goes by the
> spirit of each, rather than the letter. Seems to me OFA is designed to
> satisfy several needs, including:
>
> - protect data by disk separation
> - optimize performance by I/O balancing
> - simplfy management by providing a directory structure
>
> The way I see it, SAME attempts to cover the performance optimization. My
> personal tests (about 3 years ago) suggest that multiple SAME groups are
> recommended if there is sufficient I/O controller capability. IOW, I did
> not find SAME to be quite as performant as hand-optimization, but in
> general it's not bad.
>
> Some forms of RAID attempt to cover data protection. I strongly
> encourage RAID 1+0 over RAID 0+1. That way I get mirroring at the disk
> level, allowing individual disks to go out without losing the array. The
> 1+0 setup can then be used to provide SAME.
>
> Nothing else I see attempts to provide a standard for disk and file
> layout. So I use OFA as the basis for my disk layout, where it counts -
> making sure that Control files, Redo Log files, [S]Parameter files, and
> the like are separated appropriately (after all, RAID does not protect
> against a malicious or accidental rm -rf).

That's the sort of insight I was hoping for. Thanks.

> As far as I can tell, one really should mix and match based on
> business requirements, rather than put a foot down one way or 't'other.
>
>
> That said, to me SAME is a way of avoiding administration and
> maintenance. If you need performance, you might also need to look at
> *where* on each spindle things are running - better to take the fast
> sliver of 100 disks than take all of 10 disks.
>
>
> lol/FGB
Received on Tue Jan 04 2005 - 17:51:47 CST