Disk performance

Hi all,

as we encountered some limitations of our cheap disk setup, I really would 
like to see how cheap they are compared to expensive disk setups.

We have a 12 GB RAM machine with intel i7-975 and using
3 disks "Seagate Barracuda 7200.11, ST31500341AS (1.5 GB)" 
One disk for the system and WAL etc. and one SW RAID-0 with two disks for  
postgresql data.

Now I ran a few test as described in
http://www.westnet.com/~gsmith/content/postgresql/pg-disktesting.htm

# time sh -c "dd if=/dev/zero of=bigfile bs=8k count=3000000 && sync"
3000000+0 records in
3000000+0 records out
24576000000 bytes (25 GB) copied, 276.03 s, 89.0 MB/s

real	4m48.658s
user	0m0.580s
sys	0m51.579s

# time dd if=bigfile of=/dev/null bs=8k
3000000+0 records in
3000000+0 records out
24576000000 bytes (25 GB) copied, 222.841 s, 110 MB/s

real	3m42.879s
user	0m0.468s
sys	0m18.721s


IMHO it is looking quite fast compared to the values mentioned in the article. 
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? 

Of yourse, you can't give me exact results, but I would just like to get a an 
idea about how much faster an expensive disk setup could be. 
Would it be like 10% faster, 100% or 1000% faster? If you can give me any 
hints, I would greatly appreciate it.

kind regards
Janning