I don't know why you need to increase buffer size

It happens that several copies of this program are running simultaneously, and the all write to files on the same host. With the default buffer size, this causes too many I/O accesses, sometimes causing long delays until the actual writing operation has been completed. I would like to try weather increasing the buffer size, hence decreasing the number of simultaneous writes, would give a better performance.

I checked the link you have provided, but it doesn't give much insight into my problem (i.e. Perl version greater than 5.8, and buffered writing (not reading)). BTW, I've updated my node. If you have time, it would be great if you could have a look at it again.