SAN Transfer Very Slow..?

Hi,

I did a deployment of ESX 3.0.2 last week and the customer is now saying that the SAN performance is extremly slow. Apparently transfer rates for a 200Mb file are local to local ~5 secs, local to SAN ~40-50 secs.What could be the causeof the poor performance?

Thanks in advance

p.s. Sorry for the lack of info, I am trying to get the relevant infomation on the type of SAN, HBA's etc for the cust. And I'm not a storage expert so be gentle...