Need for more speed


5 Aug 2011
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With new USB 3.0 and SATA 6 Gb/s standards, you won’t have to wait too long for data transfers.
In the last few months, we have seen updates to two standards. One is Hi-speed USB 2.0, which has been the interface standard for peripherals and external storage devices since almost a decade, and the other is SATA 3 Gb/s, which has been around for five years or so. With the upgrade to version 2.0, the USB interface received a speed bump that was 40 times higher than its predecessor, USB 1.1. Now with SuperSpeed USB 3.0, the peak theoretical throughput has reached 4.8 Gb/s, which is ten times faster than Hi-speed USB 2.0. Such a bump was long needed because external storage devices, especially hard drive-based ones, can easily saturate USB 2.0 bandwidth. Thus, the USB 2.0 interface has become a bottleneck for external hard drives, which are capable of transferring data at more than twice the interface bandwidth. The same isn’t the case with SATA 6 Gb/s, because even today, spindle-based hard drives aren’t capable of saturating the existing 3 Gb/s bandwidth. Here, the bottlenecks are areal density and spindle speed, which can't be bumped much due to mechanical restrictions. However, solid state drives, which are faster, are gradually reaching a point at which they will fully utilize the current 3 Gb/s bandwidth, after which, they will need to move on to SATA 6 Gb/s for optimum performance.

New interfaces call for discrete controllers
Currently, there aren’t any motherboard chipsets that natively support USB 3.0. Therefore, motherboard manufactures have no choice but to include a discrete USB 3.0 controller on the motherboard. The NEC D720200F1 USB 3.0 controller, which offers two ports, is commonly seen on motherboards these days. The only chipset that natively supports SATA 6 Gb/s is the AMD 890G. Motherboards based on other chipsets use SATA 6 Gb/s controllers by Marvell to offer SATA 6 Gb/s ports in addition to SATA 3 Gb/s ports supported by the chipset. The use of on-board controllers will exist until chipsets natively support the new standards.
Good news for those who have older motherboards
No need to be upset if you have an older motherboard that doesn’t have USB 3.0 and SATA 6 GB/s ports. Add-on USB 3.0 and SATA 6 Gb/s controller cards are already available in the market and that too at very reasonable prices. So you can go ahead with your plans to buy a USB 3.0 external storage device or a SATA 6 Gb/s hard drive even though you have an older motherboard.
We received retail samples of ECS S6M2 and ECS U3N2, which are SATA 6 Gb/s and USB 3.0 add-on cards. They aren’t bigger than a credit card and utilize the motherboard’s PCIe x1 slot. Neither card requires additional power and they both come bundled with low-profile brackets for use with small form factor chassis. ECS S6M2 features a single SATA 6 Gb/s port (on the card) and an eSATA port on the rear panel courtesy Marvell 9128 controller. And ECS U3N2 is built around the NEC D720200F1 controller, which offers two USB 3.0 ports on the rear panel.

How fast is fast?
The theoretical transfer rate of USB 2.0 is 480 megabits/sec or 60 MB/s. However, full theoretical speed cannot be achieved due to the latency caused by the process in which USB transactions take place. This is also true in the case of USB 3.0, which has a theoretical transfer rate of 4.8 gigabits/sec or 600 MB/s. You can tell how fast the device is only by running benchmarks, such as file transfer tests. We set up a test PC to find out how fast an external USB 3.0 hard drive was compared to a USB 2.0 device. We also wanted to find out how fast the first SATA 6 Gb/s hard drive, the Seagate Barracuda XT, is. Our test PC comprised an Intel Core i7-870 CPU, Asus P7P55D-E Premium motherboard, and 4 GB DDR3 RAM. We chose to test the drives on Asus P7P55D-E Premium because it features support for both USB 3.0 and SATA 6 Gb/s via discrete controllers. We also tested the drives using controller cards by ECS.

USB 2.0 vs USB 3.0
Here we used Western Digital My Book 3.0 which was the first external USB 3.0 hard drive to hit shelves. We assessed its performance by first connecting it to a USB 2.0 port and then to the motherboard’s USB 3.0 port. When connected to a USB 2.0 port, the average read and write speeds were 25 MB/s and 23 MB/s respectively. But when we hooked it up to a USB 3.0 port it could read data and write data three times faster at over 90 MB/s and 75 MB/s respectively. When we connected the My Book 3.0 to the ECS U3N2 card, the read speed was almost the same, but the write performance dropped by around 20 percent. Random write speed dropped by 10 MB/s and sequential write speed dropped by 17 MB/s. The on-board USB 3.0 performance is superior, but if your motherboard doesn’t have USB 3.0 ports you can enjoy speeds twice as fast as USB 2.0 using an add-on card which costs a little more than Rs 1,000.

SATA 3 Gb/s vs SATA 6 Gb/s
The 2 TB Seagate Barracuda XT is a terrific performer. When connected to a SATA 3 Gb/s port, it read multiple files amounting to 2 GB in 16 seconds, which translates to 123 MB/s. The average write speed was 128 MB/s. HD Tach reported read and write speeds of 116 MB/s and 102.5 MB/s respectively. On switching over to SATA 6 G/s, we found absolutely no difference in performance. Infact the write performance deteriorated and average speed fell by 20 MB/s. We ran the test thrice, with a restart between tests to confirm the difference in performance. Results were similar when we switched over to the ECS S6M2 card.

Final Words
USB 3.0 looks very interesting, because it offers a tremendous performance boost over USB 2.0. Theoretically it’s 10 times faster than USB 2.0, but USB 3.0 external storage devices can transfer data three times faster, which is a very good jump for the moment. At present Western Digital My Book 3.0 (3.5-inch) and Seagate BlackArmor PS110 (2.5-inch) are the only USB 3.0 external storage devices on the market. You can expect a raft of USB 3.0 flash drives and portable hard drives by various storage device manufacturers this year.
In contrast to USB 3.0, SATA 6 Gb/s doesn’t feel very exciting, because the available hard drives don’t seem to offer any performance boost over SATA 3 Gb/s. The present spindle-based and solid state drives aren’t able to saturate the SATA 3 Gb/s bandwidth of 375 MB/s. Even high-end SSDs have a read speed of 250 MB/s. So you won’t be missing anything for at least a year or two by not upgrading to SATA 6 Gb/s, unless you’re ready to splurge on a high-end SSD.

Source : Chip magazine.
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