We are looking to purchase new 3 TB enterprise-grade drives and can buy either SAS or SATA models.
AFAIK, SAS generally gives better performance than SATA, but searching for benchmarks I found the article Seagate Constellation.2 and Constellation ES.2 Hard Drive Review .
The summary is that SATA was actually faster than SAS on most of tests. But reading through comments, it seems there is a feature called "prescan", which was apparently responsible for the low performance.
What can be recommended from a performance point of view, is it SATA or SAS? Is the real-world performance acceptable?
The kind of work-load of our systems is heavy multi-threaded sequential writing and erasing, with occasional random read access.
I believe that Womble's comment to Peter Schofield is the best observation here...these aren't true SAS disks.
No doubt you're being sold "nearline SAS", which is where they take a SATA disk and put a SAS interface on it. The drive mechanics are identical to the SATA version; only the interconnect has changed.
When you plug a nearline SAS drive into a SAS controller, it will be faster than the equivalent SATA drive because the protocols are different, and it takes a certain amount of time to convert between the SATA protocol and the SAS protocol. Wikipedia says that there can be a 30% increase in speed, but I've never delved into the protocols themselves, so I couldn't tell you.
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As an aside, I really don't know what kind of faith I'd put into those numbers. Storage Review does a pretty decent job, I think, but I can't figure out why they didn't get another drive to test when the disk started performing like this:
(source: storagereview.com)
That's a drive that should be physically identical and in terms of interface, should be performing much more in-line with the others. The fact that it shows a discrepancy like this indicates (to me, anyway), that there was something wrong with the device.
They do say that it checks out with Seagate's test suite, but I wouldn't put stock in the results until they're checked against another drive of the same model. Those results are just too weird.
Edit
Since it was brought to my attention that I didn't actually answer the question, my guess is that the SAS drive will give you better performance because of the reasons I listed above. That is what I would go with, unless research bears out the odd results that Storage Review got.
In single-user tests SATA can actually outperform SAS but once things start getting concurrent then yes SAS proves itself. So it depends on load, you don't mention your use case, for busy servers that can't cache enough of the drives content then SAS may make a lot more sense.
That said I'd ask you to consider whether these 3TB disks make much sense in a server at all, certainly if you're asking about performance and 7.2krpm disks in the same sentence anyway. In my experience you either need capacity or performance, if you want both you have to spend serious money.
Depending on your design, you might be able to get away with both: faster, smaller SAS 15K drives in a RAID 0 configuration (or possibly SSD) for your data sets that require the most I/O performance; and slower, larger SATA drives in a RAID 5 configuration for archival, less frequent storage needs.
Shedding a bit more light on your storage requirements would help you get the most out of Server Fault.
Not directly an answer to the (old) question, but here's what Seagate themselves say:
SAS mythbusters: Data highways and SAS vs. SATA
SATA drives don't have the reliability of SCSI/SAS drives (the Mean Time Before failure - MTB), so generally aren't deemed suitable for most enterprises.
Things are changing because many enterprises are putting rarely accessed data (archives) onto SATA drives on SANs, which are protected by using the appropriate RAID. But the critical stuff goes on SCSI/SAS, with the appropriate RAID. So - there's a balance to be had.