Originally Posted by pauldovi
SATA 3.0 is a marketing gimic. Hard Drives can't even fully utalize 1.5GB/s.
is not even a version or standard. There is, in point of fact, no such thing as SATA 3.0. SATA II is commonly thought of as meaning 3 Gbps performance. This is incorrect Paul and calling SATA II as SATA 3.0 is, in point of fact, a misnomer. A SATA II device or component does not have to support 3 Gbps data transfer rates to be considered SATA II. Instead, a device is SATA II compliant if it can implement some combination of standard compliant advanced features, like native command queuing (NCQ).
(Serial ATA International Organization
) is the name of the organization responsible for authoring the current SATA II specification.
These Features are below:
Features of SATA II devices and components (disk drives, adapters, port multipliers and selectors, cabling and connectors) support 1.5 Gbps and 3 Gbps data transfer rates, along with some combination of features (asynchronous notification, ClickConnect, hot plug, power management, NCQ and staggered device spin-up, among others).
NCQ is a performance enhancement for SATA II-category disk drives, and works similarly to the way command tag queuing (CTQ) works in SCSI command set-based disk drives (e.g. Fibre Channel (FC), SAS, UltraSCSI, etc). NCQ addresses the inherent inefficiencies, along with wear and tear on a disk drive due to excessive read/write head movement caused by random I/O patterns. As more I/Os arrive from more sources -- either different applications or different sources along with random I/O patterns in general -- this excessive disk head movement becomes more of an issue. As additional I/O operations arrive from different sources in a multi-stream, multi-I/O environment, more disk head "thrashing" can occur. To help cope with this issue, NCQ algorithms allow I/O operations to be performed out of order to optimize and leverage disk read/write head positioning and ultimately overall performance.
Using port multipliers, product providers can increase the number of SATA II disk drives that can attach to a single controller port. The port multiplier enables multiple SATA devices (disk drives) to fan-in (converge) to a single controller port, similar to how a switch or hub enables multiple devices to be accessed via a single port. This benefit is similar to that of FC, SAS, and UltraSCSI storage interfaces, but on a smaller scale in order to be able to have more than a couple of disk drives per SATA II controller interface. For example, SATA II supports up to 15 disk drives per controller interface, compared to the relatively small two disk limit of ATA master/slave configuration.
SAS and SATA co-existence
Not to be forgotten or lost in the discussion is the ability of SATA II devices to co-exist with SAS devices attached to a common SAS-based backplane and SAS-based controller interface. This is unique in that storage interfaces usually need to be attached to like interfaces: for example, FC to FC, SCSI to SCSI, SATA to SATA. SATA II, however, has the ability to co-exist and attach to a SAS-based controller and SAS-based backplane interconnect. The reverse is not supported, meaning that SAS devices cannot plug into SATA controllers. The benefit is that some high-performance SAS disk drives could be configured for low latency, high performance I/O, while SATA disk drives configured for storage and capacity-centric applications in the same disk shelf.