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@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 - 12:36:56 CST
