Serial ATA (SATA) & eSATA
SATA
SATA was the evolutionary replacement for Parallel ATA as it came to the end of its natural life and could no longer grow in performance and scalability. SATA is scalable and allows future enhancements to the computing platform which include easier integration, faster performance, and more efficient design. The main reason for this is SATA uses point to point technology which allows for multiple ports to be aggregated on to a controller or motherboard, up to 24 on some of today’s RAID controllers, additionally if you use port multipliers you can get up to 4 drives on a single port meaning a 4 port controller will support up to 16 drives. The benefit of this in terms of scalability and performance is obvious when you see that PATA was a parallel technology that only allowed for 2 devices per chain, one as a master and the other as a slave. Additionally the point to point nature of SATA means each device has a dedicated port which reduces the chances of bottlenecks.
The serial connection used to interconnect devices within a PC environment is much more flexible than the older ribbon cables of PATA and because of this systems can support a wider variety of devices straight from the motherboard such us HDD, DVD ROM and tape drives. In addition the reduced density of cabling allows for increased airflow so reduced heat and increased performance.
In addition to the desktop market SATA HDD has also found its way in to the NAS & SAN markets as a low cost HDD option for specific applications such as disk to disk back up and non mission critical RAID environments. Off the back of this success HDD manufacturers have been producing “Enterprise Class” solutions which are designed to work more efficiently in RAID environments traditionally seen as SCSI, SAS or FC domains, these drives are keeping performance and reliability levels up whilst reducing the cost/GB. In addition the new class of SATA drives offer many features that traditional SCSI, SAS & FC drives have such as Native Command Queuing (NCQ), enclosure management, hot plug into system backplanes and interoperability with the new SAS drives whilst being transparent to existing SCSI systems.
In its first release SATA offered speeds of 1.5Gb/s which was soon up to 3.0Gb/s second with the 2nd generation release and is the predominant SATA technology used today. There has been a 3rd generation recently announced which is currently known as “SATA revision 3.0” which will build on the success of the current generation and offer throughput of 6.0Gb/s and further enhancements the NCQ technology.
eSATA
Initially SATA was designed as an internal interface technology however due to its reliability it has been developed as an external means of connecting devices, specifically in the home and PC markets. eSATA now gives users an strong alternative to USB & Firewire (1394) interfaces with rugged shielded cables that offer distances of up to 2 metres from the host and are hot pluggable.
Applications for eSATA consist of external direct attached storage for notebooks, desktop, consumer electronics and entry servers. Many existing external hard drives use USB and/or 1394, these interfaces are not nearly as fast as SATA when compared using peak values, and can compromise drive performance.
USB and 1394 external drives are ATA drives with a bridge chip that translates from the ATA protocol to USB or 1394 protocol used for the connection. These interfaces require en-capsulation or conversion of the transmit data and then de-capsulation after the data is received. This protocol overhead reduces the efficiency of these host buses, increases the host CPU utilization or requires a special chip to off-load the host.
The results of eSATA are dramatic and lack the overhead issues associated with USB and 1394. The eSATA storage bus delivers as much as 37 times more performance, this ability is perfect for using an array of drives with performance striping behind the eSATA host port.
