Originally Posted by allikat
For HDDs, you don't need more than SATA2, you only really need SATA3 for an SSD or the SSD cached drives like the Seagate Momentus. It's possible that Deskstar will exceed the speed limits of SATA2 on occasion, but it won't be often enough to worry about.
The Momentus XT uses a single SLC NAND chip. The 500GB model maxes out at around 100MB/sec, and the 750GB model maxes out at around 190MB/sec. (Actually, a bit lower)
SATA2 is overkill for one of those. I think that's why they are SATA2 rather than SATA3? It's not like the XT is a SATA3 SSD, which has at the minimum 8 NAND chips. (All capable of those speeds)
Btw, SATA bandwidth is per-channel/port. Although some controllers are limited by their link to the CPU, the newer AMD boards can push through around 2GB/sec
That's enough for 3-4 SATA3 SSDs in RAID-0!
Originally Posted by ghostrider85
Okei but what aspects do You look in HDD to know that?
RPM, latency and cache, i think?
Sequential speeds, access times, RPM.
RPM doesn't affect much, but higher RPM drives also have more aggressive seeking. Technically you could make a 5400RPM drive that seeked only a few miliseconds slower than Raptors (~6ms), but they don't want to do that. Manufacturers tune the drive to whatever speed they want, and use the RPM as a marketing stat which reveals some of the performance characteristics of the drive.
It's pretty obvious that RPM doesn't matter when you can get a 5400RPM Seagate laptop drive with 17.2ms access times, 7200RPM Seagate laptop drive with 17.2ms access times, and a 5400RPM WD Green 2TB (WD20EARX) with 15ms access times. But that said, RPM usually goes hand in hand with access times. Most 5400RPM drives are closer to 20ms, most 7200RPM are closer to 13ms, and most 10k RPM drives are closer to 7ms.
Look at the access times and sequential speeds. If you divide 1000 by the access times, that gives you an IOPS (I/O's per second) figure for how many small reads/writes a drive can perform (on average) within a second. For a 5400RPM drive it might be 50-60 IOPS. For 7200RPM, 70-80 IOPS. For a 10k RPM Raptor, ~150IOPS. (three times faster than a Green) For an SSD it's probably between 2000 and 200,000, depending on the quality of your SSD controller.
Stuff like how well a drive deals with multitasking scenarios is unadvertised. At best you can comb over reviews/benchmarks to try to figure it out.Edited by Kramy - 2/28/12 at 6:30pm