My initial response (as always) is How to prove it's a SAN problem[/url] by Brent Ozar.
If it really is the SAN causing the problems, there is a lot of things to look into. Among these are caching, RAID levels, any failed drives, how many spindles your LUN spans, what other LUNs are using the same spindles and so on. Not to mention, is it VMware which states that the write latency is 50ms, or the guest OS? Virtualization makes performance troubleshooting a bit more "interresting".
Ole Kristian Velstadbråten Bangås -
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TwitterConcatenating Row Values in Transact-SQL[/url]