On Thu, 28 Aug 2003, Sean Chittenden wrote:
> > What it still leaves quite open is just what happens when the OS has
> > more than one disk drive or CPU to play with. It's not clear what
> > happens in such cases, whether FreeBSD would catch up, or be "left
> > further in the dust." The traditional "propaganda" has been that
> > there are all sorts of reasons to expect PostgreSQL on FreeBSD to
> > run a bit faster than on Linux; it is a bit unexpected for the
> > opposite to seem true.
>
> Let me nip this in the butt before people run away with ideas that
> aren't correct. When the tests were performed in FreeBSD 5.1 and
> Linux, the hard drives were running UDMA. When running 4.8, for some
> reason his drives settled in on PIO mode:
>
> ad0s1a: UDMA ICRC error writing fsbn 1458368 of 729184-729215 (ad0s1 bn 1458368; cn 241 tn 12 sn 44) retrying
> ad0s1a: UDMA ICRC error writing fsbn 1458368 of 729184-729215 (ad0s1 bn 1458368; cn 241 tn 12 sn 44) retrying
> ad0s1a: UDMA ICRC error writing fsbn 1458368 of 729184-729215 (ad0s1 bn 1458368; cn 241 tn 12 sn 44) retrying
> ad0s1a: UDMA ICRC error writing fsbn 1458368 of 729184-729215 (ad0s1 bn 1458368; cn 241 tn 12 sn 44) falling back to
PIOmode
>
> The benchmarks were hardly conclusive as UDMA runs vastly faster than
> PIO. Until we hear back as to whether cables were jarred loose
> between the tests or hearing if something else changed, I'd hardly
> consider these conclusive tests given PIO/UDMA is apples to oranges in
> terms of speed and I fully expect that FreeBSD 4.8 will perform at
> least faster than 5.1 (5.x is still being unwound from Giant), but
> should out perform Linux as well if industry experience iss any
> indicator.
Plus, in most "real" servers you're gonna be running SCSI, so it might be
nice to see a test with a good SCSI controller (Symbios 875 is a nice
choice) and a couple hard drives, one each for WAL and data. This would
more closely resemble actual usage and there are likely to be fewer issues
with things like UDMA versus PIO on SCSI.
