What Steve Jones said, except that I wouldn't entirely rule out RAID5 - it's suitable for a workload heavily biased towards reads with little/no write activity and lower recovery SLAs, maybe a second tier large read-only DB or staged reporting DB with infrequent data loads. EDIT: Actually you said OLTP so forgot this part - RAID5 has no place here.

@pdross2000:

I think you are thinking of RAID0. RAID1 can survive a single disk failure just fine with no outage.

@robert.concepcion:

I generally wouldn't recommend any NAS solution - having a file-level network redirector between your server and the data files is asking for trouble. Go for SAN or DAS - data files on NAS is a pretty narrowly supported scenario from MS. That said NetApp have a SAN (block-level) solution in most of their products don't they?

Regards,

Jacob