increasing blocksizes decrease performance in Gbit

[Zoltan Bogdan]

Hi,

does anyone know about the performace impact whereabouts of different 
blocksizes?

I'm using kernel 2.4.18 on a machine with 512MB Ram and two 3Ware
Escalade 
7850 controllers with an 8-Disk (hardware- )RAID 5  array on each. 

A softraid 0 Array spans  those two Raidarrays.     

While doing some benchmarks over Gbit Network I experianced the
following:
  
Block | Read Lin | Read Rnd | Write Lin
 kB   |  MB/sec  |  MB/sec  |  MB/sec  
------+----------+----------+-----------
   16 |    25.9  |     3.3  |    12.1
   32 |    31.5  |     6.6  |    17.8
  256 |    15.4  |    13.2  |    21.3
 1024 |    13.7  |    20.8  |    21.4

Any clue why the value for linear read decreases when the Blocksizes get
higher?

I thought the contrary to be true.

I apologize if my question I to off topic.

Thanks 
z