Originally posted by tamilselvan
To find out OS block size, login as sys and run the following query:
select max(lebsz) from sys.x$kccle;

If Veritas is used and block size is 8k, then it is advisable to set your DB_BLOCK_SIZE to 8K. The reason is simple: no extra IO.
When they are NOT equal then OS has to do reconstruct the data block in the memory. This will impair performance.

Tamil
I'd like to see some supporting evidence -- i don't believe that any overhead that might be associated with this block reconstruction would be enough to offset the loss in i/o performance from larger block sizes.