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Home -> Community -> Usenet -> c.d.o.server -> Re: OFA Architecture with RAID
I agree, I have always heard that RAID 5 is noticeably slower. What if I have, for example, a
large database that is primarily just read-only? I'd update the data (significantly) once per
week, but the users would be doing queries, not generating a lot of new data. Is RAID 5 and
advantage, neutral, or a disadvantage in this case? Just curious.
Mike
Steve Phelan wrote:
> Well, not really. The problem with RAID5 arrays is their generally very poor write
> performance. Of the 3 RAID5 arrays I've tested this has been 50-200% slowdown compared to
> tqking the same drives in a striped array (i.e. RAID0). A write cache can get round this, but
> this is a dangerous route to take if you lose power to the server - potential database
> screw-up.
>
> The problem is that much of your database may actually be very write intensive, especially
> redo, archive, temp and maybe your datafiles if that's what your application is like.
> Distributing the I/O is good, but mixing eveything together and hoping that the RAID5 array
> mix will some how sort it all out is not the way to go. A database's I/O is a far more
> complex mix, and you've got to be prepared to make some intelligent loaction decisions.
>
> Like I said, best thing is to try it and monitor it. Start moving things around when you see
> bottlenecks and then re-monitor.
>
> Regards,
>
> Steve Phelan
>
> (Oracle 7 & 8 OCP)
>
> gremlin wrote:
>
> > Well, that was my thinking with the one mount point. If the file system is RAID (5 or 3)
> > then you really don't get anything by having different mount points, they all end up as
> > one in the end anyway! I would think this would give very good performance, if you have
> > n physical drives and n processors then the I/O is distributed as much as you can get it,
> > isn't it? If you split it up (say, index tables on 2 drives and data tables on 3
> > others?) then you still wait for the slowest one anyway I would think. Not that I claim
> > to be any kind of expert.
> >
>
> [snip]
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