How to change the block size in linux

[kamesh jayachandran <kameshj@xxxxxxxxxxxxxxx>]

I have seen block size in my linux as 4k.In my college it is 1k block.In one 
of my remote server it is 512 bytes.My question is how to change the block 
size .Which size is better.What is the relative merits of each one
Thanks in advance
kamesh jayachandran

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