hard drivesassatawindows-server-2003
SATA 3 hard disk can be connected to SAS ports. But If i connect SATA 3 drive to a SAS port then can i get same speed as SATA 3 originally offers or will it be a difference? Will it reduce the performance than connecting to a SATA 3 port.
I have a intel server board which has more number of SAS ports and i have to connect my SATA 3 drives to these SAS ports.So i am concerned about the performance. So please help me on this
If the SAS controller supports sata3 you can, If not it will go back to sata2. If the disk is not a SSD or in a raid you will never get sata3 or sata2 max speeds
Name on your sas controller ?
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.
Best Answer
The first thing that should be noted is that for most practical workloads of a single mechanical disk, even SATA1 which offers a transfer rate of 150 MB/s would not present a bottleneck. The higher transfer rates are mainly relevant for either cached I/O or high-performance SSDs. The first case is rare enough not to make a significant difference in overall performance. The latter case is only a concern if your SSD actually is performing better than the link can handle even over a long term (SSD performance typically degrades as the disk fills up). So unless you are building a corner-case setup, you would not notice a performance difference, no matter the link speed.
Now the technical part: there are two SAS standards - the older SAS 1 with a data rate of 3 Gbps and the newer SAS2 with a data rate of 6 Gbps per link. Both include SATA compatibility. SAS1 controllers would negotiate SATA2 speeds (300 MB/s) with connected SATA devices. Most newer SAS2 controllers will negotiate SATA3 speeds (600 MB/s) with capable devices. You should simply consult your controller's documentation / spec sheet to see what it would support.