Re: RAID: Advantage or disaster?

Generally mirrors will give read benefits (using round-robin scheduling or even bouncing the request at both and seeing which comes back fastest), and minimal write penalty since the writes are done in parallel.

But I do disagree with Dusan's assertion that stripes aren't good.

Cheers
Connor

"Vladimir M. Zakharychev" <bob_at_dpsp-yes.com> wrote in message news:9uodll$5md$1_at_babylon.agtel.net...
> Ahem... Correct me if I'm off the track, but isn't RAID 1 a mirroring?
This
> said, I can't see how RAID 1 can improve PQs by reading off 2 disks in
> parallel unless the RAID controller is so smart it interleaves disk reads
> between the mirrors. Anyway, from Oracle's point of view these two are
> one so it will read from them (it) sequentially, wouldn't it?
>
> --
> Vladimir Zakharychev (bob_at_dpsp-yes.com)
http://www.dpsp-yes.com
> Dynamic PSP(tm) - the first true RAD toolkit for Oracle-based internet
applications.
> All opinions are mine and do not necessarily go in line with those of my
employer.
>
>
> "Dusan Bolek" <pagesflames_at_usa.net> wrote in message
> news:1e8276d6.0112060035.70cdfe5c_at_posting.google.com...
> > peacocda_at_yahoo.com (Dan Peacock) wrote in message
> news:<67044b3b.0112051400.524933c9_at_posting.google.com>...
> > > I'm going to disagree with your assertion.
> >
> > I'm going to disagree with your, so it's OK. :-)
> >
> > > If you have only a few
> > > data files, you cannot take advantage of parallel query without a
> > > striped set of some kind as you will bottleneck on a single spindle
> > > and have idle processes that are doing nothing but waiting. Now, I
> > > used to be a RAID5 is great always zealot. I've since modified that
> > > stance, but I will say this: most applications are read intensive, and
> > > it's a documented fact that RAID5 sets are very good at reading data
> > > off the disk.
> >
> > Maybe I'm wrong, but I think that you can have as much of datafiles as
> > you need. So If you want to take advantage of PQ, then you can have
> > tablespace with ten datafiles across ten disks.
> > If you're using RAID1 you can use PQ, because you already have your
> > data on two disk and can read from them in parallel.
> > The problem with RAID5 is that your files are not spread according to
> > your needs, but by internal mechanism. So is hard to tune your I/O
> > access by spreading across the disks, because you never know where
> > your files are.
> > The worst scenario is to use one RAID5 set for all datafiles, that's
> > very bad and I've seen it for many times.
> > The biggest advantage of RAID5 is the price for it. RAID1 is more
> > expensive because of disk prices and even more because of disk slot
> > prices. So If you have only few disk bays and can't afford bigger
> > server or external storage, then using RAID5 for some large tablespace
> > is definitely a good option. Just do not use RAID5 for redologs and
> > temp and do not put your index tablespace on the same RAID5 set as the
> > data tablespace, because you can realize that your indexes will be on
> > the same disk with appropriate data, because Murphy´s laws are
> > working. :-)
> >
> > --
> > _________________________________________
> >
> > Dusan Bolek, Ing.
> > Oracle team leader
> >
> > Note: pagesflames_at_usa.net has been cancelled due to changes (maybe we
> > can call it an overture to bankruptcy) on that server. I'm still using
> > this email to prevent SPAM. Maybe one day I will change it and have a
> > proper mail even for news, but right now I can be reached by this
> > email.
>
Received on Thu Dec 06 2001 - 17:07:23 CST