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Tech blog  October 2, 2015

Form factor (SATA/SAS/NVMe/PCI Express Card/M.2)

Introduction

There are several ways to connect solid state drives (SSD) to your devices, including SATA (serial ATA), SAS (Serial Attached SCSI), NVMe (Non-Volatile Memory Express) and PCIe (Peripheral Component Interconnect Express). At the consumer level, SATA is the most widely used form factor and most modern PCs come equipped with multiple SATA ports. When looking at the enterprise side of things, SAS dominates the market. Looking ahead, NVMe will likely to emerge as the de-facto form factor as prices begin to fall.

SATA was brought about in the year 2002, and took the place of the former market leader parallel ATA (PATA), which itself came as a result of a long train of incremental technological advancements dating back to the original AT Attachment interface. SATA was developed as a natural method to reduce costs and boost performance across the board. The various enhancements went beyond simple speed increments; a slew of new features were introduced to make the transition more necessary.

To replace PATA as the dominant bus in the market, SATA implemented various relevant benefits. Cutting down the large cumbersome cable from the old PATA design was one of the main attractors. In contrast, SATA is a serial device, meaning the amount of wires needed to carry information from host to storage device was dramatically decreased. The special distinguishing feature of serial wires is that wires can carry information in dual directions, meaning less wires are needed. This change allowed SATA to use a smaller, more flexible cable that could extend out much farther (1 meter versus 18 inches). Utilizing a smaller cable saved on motherboard space, and also allowed for more airflow and easier configuration within computer chassis. The speed of ATA devices also increased dramatically under the new serial method. New iterations of SATA have allowed it to reach speeds of up to 6Gbits/s (600MB/s). SATA was created for the sole purpose of providing a better storage solution and it delivered in spades, leading PATA technology in every measurable category.

SATA's benefits extend to all facets of usage, including through both enterprise and consumer level. Though the main attractors do lend SATA to a more consumer-centric usage rate, enterprise still sees so me benefit from using SATA interface, namely cutting down on costs. Depending on application, it may behoove the user to opt for the cheaper alternative and use SATA instead of the other more costly methods.

One such alternative is Serial-Attached SCSI (SAS), the current leader of network-attached devices for enterprise environments. SAS, like SATA, is currently being used for both hard disk drives and solid state drives (SSDs). SSDs connected via SAS are generally enterprise class because of their higher top speed (up to 12Gbits/s), their much higher price, and their higher reliability. SAS was created to be backwards compatible with SATA, so SATA drives easily fit into SAS connection ports. Just like with the ATA protocol, SAS began as a parallel SCSI interface, only later implementing serial compatibility and vastly increasing their performance.

As history has always indicated, technology is always lapsed by the slow trickle of advancements. SATA will be around for another half decade or so more, but it will eventually be replaced by a new form factor that is currently in its infancy: Non-Volatile Memory Express (NVMe). NVMe completely revamps how the computing world utilizes storage devices. Instead of creating a new interface to connect into, NVMe utilizes the already-in-place PCIe lanes. Using existing infrastructure means future implementation of NVMe devices will be seemingly painless, though other issues always impede the migration to new technological advancements (in this case software that was originally created to work well with SATA devices). Once the proper adjustments have been made, this new interface will lead the charge into a new future with speeds of up to 2GB/s. Until then, however, we can use the Serial SCSI interface for our enterprise needs.

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