eSATA is a physically-modified interpretation of Serial ATA, optimized for external devices. The connectors are slightly different, and the minimum voltage levels are increased to ensure reliable operation. Depending on the SATA controller, eSATA supports either 1.5 Gbit/s or 3 Gbit/s operation, resulting in 150 and 300 MB/s bandwidth using 8/10-bit encoding. The practical limitations are the maximum cable length of 2 meters, and controller support via your operating system—devices using the Advanced Host Controller Interface (AHCI) are the most flexible. eSATA is much faster than USB 2.0 (480 Mbit/s) or FireWire 1394a and 1394b (400/800 Mbit/s).
On May 25, the SATA IO (SATA International Organization) released revision 3.0 of the SATA specification, which doubles throughput from 3 to 6 Gbit/s (600 MB/s). The new spec lets you continue using existing cables, but the SATA IO recommends high-quality cabling for the sake of data integrity and performance. SATA 3.0 also introduces a low insertion force (LIF) connector for consumer devices, and modifications to command queuing: NCQ Queue Management allows altering the order of pending commands, while NCQ Streaming utilizes this feature to optimize for isochronous transfers. However, SATA 3.0 still does not address power over SATA (eSATAp), and it does not yet include 6 Gbit/s transfers for external devices. Hence eSATA will remain at 300 MB/s for a while, and without the ability to supply power through the data port.
eSATA Utilizes USB to Power External Devices
Of course, the interim solution for external devices is to get power in some other way. Using an external power supply would not make a lot of sense for thumb drives, which are meant to be ultra portable. Hence the only solution lies in accessing existing interfaces such as USB 2.0. All three eSATA drives we reviewed are combo drives, meaning that they support either eSATA or USB 2.0 through different interfaces. All three utilize JMicron’s JMB362 controller, which supports both standards. If you connect USB 2.0 first, the drive will establish a USB 2.0 connection and use it for power and data. To use eSATA you have to plug in that connector first, and create a USB 2.0 connection using a dedicated USB 2.0 cable to get power to the unit.
eSATA + USB
The MSI 790FX-GD70 motherboard we used to test the devices offers an enhanced eSATA port with additional pins for USB 2.0 power supply, which the three eSATA drives support. Although this is not specified by the SATA IO, the approach worked fine during our testing.
- New Thumb Drives With eSATA And High Capacities
- Introducing eSATA… Kind of
- 128 GB And USB 2.0: Kingston Data Traveler 200
- 32 GB, eSATA/USB: Maxell Solid State Drive
- 8 GB, eSATA/USB: OCZ Throttle eSATA Flash Drive
- 32 GB Silicon Power eSATA/USB SSD
- Test Setup And Access Time
- Throughput Results
- I/O Performance Results