Re: ORACLE8 NT and RAID5

Hi

Does anyone have general guideline/practice on the best way to configure RAID for database devices ?

Specifically, from articles I read on RAID, it seems to be saying:

1. if your database is OLTP and update intensive, you want to stay away from RAID5 (I assume due to the additional write to parity disk).
2. Likewise, I have read conflicting suggestions where someone would recommend RAID5 since it's great for random access (read) but then someone else would not since when there is disk failure, RAID5 read performance would degrade greatly (having to generate missing disk data from parity and stuff).
3. I also read something that if your database is DSS and makes extensive use of sort areas and temporary tables, then RAID10 (0+1) is the best options. And if this storage are transient (only valid during execution of a sort/join), then you could just use RAID-0 striping.

Does this mean that for tempdb, we could just use RAID-0 configuration (or maybe just by-pass RAID altogether and set it up on a file system) ?

And what about the log devices ? Since we need to ensure it's recoverability, we could either use RAID1 or RAID5 or RAID10. If we have the extra disk capacity, would RAID1 be the way to go ? Or would RAID10 be actually better ?

For data that are predominantly DSS (but do get updated as a nightly batch), should we use RAID5 then ? Or if we do have extra disks, just use RAID1 as well ? Or is there a better configuration ?

For data that will be updated somewhat frequently and need to be redundant/mirrored, it seems to be a choice between RAID1 and RAID10. (I was told RAID1 write performance isn't too bad, especially for Clarion RAID and using write cache).

So if we have the extra disk capacity, it sounds like we could just configure pretty much everything for RAID1 (with exception of the tempdb). Is RAID10 a better option than RAID1 only if you care about expense (since RAID1 requires more disk) or does it actually offer better performance ?
Does RAID5 offer better performance than RAID1 or RAID10 in any area ?

If someone can help dispell any misunderstanding/myth on this, it would help us greatly. Thanks

Zen

In article <01bed1d4$5d8d8420$ce1e1dac_at_ut9811252159>,   "Kaboel Karso" <karso_at_kpn.com> wrote:
> hi,
>
> RAID0 = striping
> RAID1 = mirroring
> RAID2 = duplexing
> RAID5 = striping with calculation of the parity bit placed on all the
disks
> participating in the raid volume using these in a round robin fashion
> RAID10 = striping & mirroring
>
> Saying that, you should investigate what the different raid levels is
> actually doiing. For performance reasons RAID0 is preferrable. As for
> reliability, you must have some sort of protection. The best scenario
is
> using RAID10 (RAID 1+0). btw, there is a difference between RAID 0+1
and
> RAID 1+0 , not performance wise but in case of a disaster.
>
> Imo, the next best scenario is to use RAID5 for the datafiles and
place all
> other files causing sequential writes e.g the redo logfiles, on a non
> raided disk. The redolog files preferrably mirrored by Oracle.
>
> I found some whitepapers on this topic on the SUN website a while ago.
> Maybe they're still available.
>
> Kaboel
>
> dcoan_at_aegonusa.com schreef in artikel <7mo0dg$obe$1_at_nnrp1.deja.com>...
> > In article <7mnmu1$k2i$1_at_nnrp1.deja.com>,
> > drfuller1_at_my-deja.com wrote:
> > > We are currently configuring a new NT server for our Oracle8
database
> > > and I would like to know the pros or cons of using raid5 ot if
anyone
> > > has a better recommendation, it would be appreciated.
> > >
> > > Thanks,
> > > Don
> > >
> > > Sent via Deja.com http://www.deja.com/
> > > Share what you know. Learn what you don't.
> > >
> >
> > A subject near and dear to my heart...... We are Oracle 7 nd 8 on NT
> > also.
> >
> > All raids give about the same level of fault tolerance.
> >
> > We recently had the opportunity to do some performance comparing of
RAID
> > levels in a real world environment using both compaq and EMC dasd.
Here
> > are the results:
> >
> > Raid Level - Cycle times
> > Raid 5 (EMC RAID S) - 23 hours
> > Raid 1 (EMC) - @12 hours
> > RAID 10 (0+1) (Compaq) - @11 hours
> >
> > We never did RAID 10 on EMC because of the minimum stripping size on
> > EMC. However, I still think that would have given us the best
> > performance.
> >
> > We also have a Sybase serrver where performance of a query went from
1
> > hour to about 9 minutes by just going from RAID 5 to RAID 10.
> > (SERIOUSLY!!)
> >
> > Of couse the EMC DASD costs about 10-20 times the compaq and has
@5GB of
> > cache, so we were surprised to see such a giant timing difference,
but
> > it was there and proven several several several times using several
> > servers and Oracle configs.
> >
> > DASD vendors and people will give you the old 'But everything is
comming
> > from disk Cache' and 'You don't understand how OUR Raid 5 works' and
the
> > ever famous 'let me show you this white paper' arguments. DON'T FALL
FOR
> > IT!!!!!!! Simply, tell them to prove it on your DB in your shop.
> > Perhaps in your envinment with your DB (ie a DSS db) the performance
hit
> > will not be too bad.
> >
> > In General:
> > Raid 5 - SLOW, least expensive
> > RAID 1 - Fast, More expensive
> > RAID 0+1 - Fastest, Same expence as RAID 1
> >
> > Other RAIDs - not really worth mentioning. Avoid them.
> >
> > On a RAID 5 array, performance will degrade more than on other RAIDs
if
> > a drive fails.
> >
> > Bottom Line Recommendations:
> > - More spindles are better.
> > - Stripe the data across spindles.
> > - If you can afford it go RAID 10 (0+1) DO IT!!!
> > - Aviod OS level striping - Do hardware level
> > - Raid 1 is an ok alternative, but requires more support as far as
> > placement is concerned to get the performance.
> > - Only use RAID 5 when ..... Well - Just don't unless you have NO
other
> > choice and you prove the performance is acceptable and you can live
with
> > it forever. Remember - The choice you make today becomes tomorrows
> > 'thats we way we have always done it' and it is used everywhere.
> >
> > WOW - How high can I stack this soapbox? :-) Good luck.
> >
> > Doug Coan
> > Senior Client Server System Integrator
> > AEGON USA
> > dcoan_at_aegonusa.com
> >
> >
> > Sent via Deja.com http://www.deja.com/
> > Share what you know. Learn what you don't.
> >
>

Sent via Deja.com http://www.deja.com/
Share what you know. Learn what you don't. Received on Fri Jul 23 1999 - 08:55:23 CDT