Re: Disk performance

Janning wrote:
> IMHO it is looking quite fast compared to the values mentioned in the article.
>

The tests in the article were using the 2006 versions of the same drive
you have, so I'd certainly hope yours are faster now.

> What values do you expect with a very expensive setup like many spindles,
> scsi, raid controller, battery cache etc. How much faster will it be?
>

If you visit look at my "Database Hardware Benchmarking" talk at
http://projects.2ndquadrant.com/talks I give examples of some of this.
Page 9 shows how much of a speedup I saw going from one cheap drive to
three for example, and P32 shows that in the mixed I/O bonnie++ seeks
tests tripling the number of drives increases the seeks rating it
computes from 177 to 371.

If you add in a RAID controller, the sequential read/write numbers
increase no differently than if you add disks with software RAID. They
do significantly increase what I call the "Commit Rate", which is how
many small writes you can get per second for database commits. The
commit rate for regular drives is proportional to their rotation rate,
between 100-250 commit/second without a battery-backed RAID controller.
As you can also see on P32, it jumps to thousands of commits/second with
one.

Presuming you have reasonable sequential performance and a
battery-backed controller to make the commit rate reasonable, database
applications will then normally bottleneck at how fast they can seek
around. It is extremely hard to estimate how fast that scales upwards
as you add more disks to an array and insert a read/write cache into the
system.

--
Greg Smith 2ndQuadrant US Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com www.2ndQuadrant.us