Re: RAID 0 not as fast as expected

On Thu, 2006-09-14 at 16:35, Craig A. James wrote:
> Alan Hodgson wrote:
> > On Thursday 14 September 2006 11:05, "Craig A. James"
> > <cjames(at)modgraph-usa(dot)com> wrote:
> >> I'm experiment with RAID, looking for an inexpensive way to boost
> >> performance. I bought 4 Seagate 7200.9 120 GB SATA drives and two SIIG
> >> dual-port SATA cards. (NB: I don't plan to run RAID 0 in production,
> >> probably RAID 10, so no need to comment on the failure rate of RAID 0.)
> >>
> >
> > Are those PCI cards? If yes, it's just a bus bandwidth limit.
>
> Ok, that makes sense.
>
> One SATA disk = 52 MB/sec
> 4-disk RAID0 = 106 MB/sec
>
> PCI at 33 MHz x 32 bits (4 bytes) = 132 MB/sec.
>
> I guess getting to 80% of the theoretical speed is as much as I should expect.

Note that many mid to high end motherboards have multiple PCI busses /
channels, and you could put a card in each one and get > 132MByte/sec on
them.

But for a database, sequential throughput is almost never the real
problem. It's usually random access that counts, and for that a RAID 10
is a pretty good choice.