Re: NT Oracle database with RAID-5 hardware controller - Is it good?

In article <35b88469.0_at_news.webt.com>,
  "bubba" <brittonb_at_webt.com> wrote:
> That really doesn't make any sense whatsoever.
>
> We have an oracle 8 server(hp) using raid 5(adaptec aaa-131, 3 4.5g drives
> with spare.)
>
> Performance is very good.
> With RAID 5 at the hardware level, information is READ, the hard ware
> controller will spin all of your RAID 5 drives to retrieve this information.
> This is like having 3 drives work in conjunction to retrieve each a piece of
> the information you ened from your oracle database. Since much of doing
> database work is running queries, performance can be very good. However,
> contrast that with WRITEing to the database. The HW controller has to split
> the information up, create a check sum, and split that information across
> the drives. This can be a bit slower in writing.
>
> So, in layman's terms:
>
> READING: Fast

Read operations will be faster

> Writing: A little slower.

RAID 5 should not be used for write-intensive files, since the continuous calcultation of ECC's makes data-write operations slower ( htis in turn depends on how complex the ECC implementation is) - RAID 3 is a good alternative.

>
> But don't forget one of the primary purposes of RAID 5: Fault tolerance. if
> one of the drives fail, your still up and running. And if you have a hot
> spare, it will automatically bring it on line in the event of a bad drive.
>

If complete reduncy of data is required you'd have to use RAID 1.

The striping of data across several drives has other consequences besides balancing I/O. One advantage is that logical system files may be created which are larger than the maximum size normally supported by an operating system - the disadvantage is, however, that it is no longer possible to locate a single datafile on a specific physical drive. This may cause the loss of some application tuning possibilities. Database recovery can also be more time-consuming. If one physical disk needs recovery - all the disks which are part of the logical RAID device must be involved in the recovery.

Datafiles and archives can be placed on RAID arrays since they are accessed randomly. Redo logs should *NOT* be put on RAID arrays since they are accessed  sequentially and therefore performance is enhanced having the disk head near the last write location. Mirroring of redo logs, however is strongly recommended.

Oracle recommend RAID 1 rather than RAID 5.

Having said all that, there don't seem to be any perceptible performance problems with our Oracle servers under RAID 5. (DIGITAL PRIORIS / AIX) where each individual disk size is 2.5 Gbyte. One of the new servers which will come in shortly will be RAID 1 though with each disk 10Gbyte.

> fantail2 wrote in message <6p8jri$bjo_at_tandem.CAM.ORG>...
> >I just heard that if you install an Oracle database on a COMPAQ ProLiant
> >with a RAID-5 disk controller, the performance of the database is greatly
> >reduced.
> >
> >Can someone can explain to me why?
> >
> >Thanks!
> >
> >
> >
>
>

--
Oliver Willandsen
European Commission
http://europa.eu.int
All remarks are my own and do not necessarily reflect offical European Commission policy

-----== Posted via Deja News, The Leader in Internet Discussion ==----- http://www.dejanews.com/rg_mkgrp.xp Create Your Own Free Member Forum Received on Mon Jul 27 1998 - 09:33:57 CDT