Re: H/W RAID 5 on slower disks versus no raid on faster HDDs

raid 0 (striping) spreads the load over multiple spindels, the same way raid 5
does. but raid 5 always needs to calculate parity and write that to it's
parity drive.

RPM isn't that critical, a lot depends on the machine, the processor and the
memory (and the spped with which the processor can get to the memory). I have
recently tested a lot of systems with some database benchmarks we wrote here
at work. We're not running Postgres here at work, sorry, these benchmarks are
of no use to Postgres ...
We we found is that a lot depends on motherboard design, not so much on drive
speed. We got to stages where we allocated 1.8 GB of RAM to shared memory for
the database server process, resulting in the entire database being sucked
into memory. When doing reads, 100% of the data is coming out the that
menory, and drive speed becomes irrelevant.

From tests I did with Postgres on my boxes at home, I can say: The more shared
memory you can throw at the server process, the better. Under MacOS X I
wasn't able to allocate more than 3 MB, Under Linux, I can allocate anything
I want to, so I usually start up the server with 256 MB. The difference? A
process which takes 4 minutes under Linux, takes 6 hours under MacOS - same
hardware, same drives, different memory settings.

Best regards,
Chris

On Thursday 21 November 2002 12:02, you wrote:
> Thanks Chris,
>
> does raid0 enhances both read/write both?
>
> does rpms not matter that much?
>
> regds
> mallah.
>
> On Thursday 21 November 2002 22:27, you wrote:
> > RAID 5 gives you pretty bad performance, a slowdown of about 50%. For
> > pure performance, I'd use the 3 18 GB drives with RAID 0.
> >
> > If you need fault tolerance, you could use RAID 0+1 or 1+0 but you'd need
> > an even number of drives for that, of which half would become 'usable
> > space'.
> >
> > Best regards,
> > Chris
> >
> > On Thursday 21 November 2002 11:45, you wrote:
> > > Hi folks,
> > >
> > > I have two options:
> > > 3*18 GB 10,000 RPM Ultra160 Dual Channel SCSI controller + H/W Raid 5
> > > and
> > > 2*36 GB 15,000 RPM Ultra320 Dual Channel SCSI and no RAID
> > >
> > > Does anyone opinions *performance wise* the pros and cons of above
> > > two options.
> > >
> > > please take in consideration in latter case its higher RPM and better
> > > SCSI interface.
> > >
> > >
> > >
> > > Regds
> > > Mallah.

--
Network Grunt and Bit Pusher extraordinaire