Start with this simple fact: On a rotating drive, the optimum location for storing data is on the outside tracks, where the throughput is at its highest as the disk spins. That data rate may reach 250 megabytes per second (MBps), or 2,000 megabits per second (Mbps), in 2011, more or less saturating the current 3Gbps limit of the SATA 2.0 specification. But that won’t be a problem for another year and a half, right?

Rightfor rotational media. But the ever-increasing speed and popularity of flash-based solid-state drives (SSDs) throws a wicked-fast monkey wrench into the equation, and underscores the need for SATA 3.0. Today.

But the real benefactors of the 6-Gbps interface are SSDs, which stream data instantly from flash memory at tremendous throughputs. Take, for example, the new Corsair Extreme Series of high-performance SSDs. The press release touts the speed of the drives: “Built using the renowned Indilinx Barefoot controller and Samsung MLC NAND flash memory, the Extreme Series has been designed to offer the highest performance currently available on the market, with read speeds of up to 240 MBps and write speeds of up to 170 MBps.” 240 MBps is 1,920 Mbps, or 1.9Gbpsdangerously close to that theoretical limit of SATA 2.0. And that’s just one drive. String two or more into a striped RAID 0 array (Corsair notes that these drive are ideal for enthusiasts looking to do just that) and you can expect performance to increase still further. RAID Level 0 doesn’t simply double your bandwidth, of coursethere’s overhead as the RAID controller plays traffic cop, and that cuts into things. But an improvement of 30 or even 20 percent would dangerously tax SATA 2.0.

The problem gets worse with today’s news from Intel of the X25-M Mainstream SATA SSD, based on the industry’s first 34nm NAND flash memory. Intel makes impressive performance claims for this new drive: “Featuring the latest-generation native SATA interface with an advanced architecture employing 10 parallel NAND Flash channels, our high performing SSD is architected with powerful Native Command Queuing to enable up to 32 concurrent operations. Other features include low write amplification and a unique wear-leveling design for higher reliability and longer lasting performance.” These drives claim to offer 250-MBps sustained sequential reads, and sustained writes of up to 70 MBps.

The new, bandwidth-doubling specification of SATA 3.0 was finalized in May. Additional features include a new Native Command Queuing (NCQ) streaming command to enable isochronous data transfers for bandwidth-hungry audio and video applications, improved power management, and a new connector for 1.8-inch drives. Good thing it’s done, right? We should see chips on motherboards any day now, right? No sir.

As we reported early last week, Marvell Semiconductor (somehow the only manufacturer making SATA 3.0 chips) confirmed an issue with its 6-Gbps 88SE9123 chip. Since then, both Asus and Gigabyte have reportedly decided to remove the technology from their upcoming Core i5/”Lynnfield” motherboards, Asus stripping down the P7P55D and Gigabyte an unnamed board.

Interestingly, the problems seem to lie not with the SATA 3.0 elements in the chip but with PATA compatibility. According to an email from a Marvell spokeswoman, “Recent news of delays of SATA 6Gb/s product launches is due to a hardware issue related to PATA (legacy Parallel ATA, or IDE) compatibility on the Marvell 88SE9123. This Marvell controller chip supports both 6Gb/s SATA as well as PATA [Parallel ATA] on the same chip. It is the legacy PATA functionality, not the SATA, which is the root cause of the product delays.” Whatever the cause, it’s slowing things down, although Marvell still plans to release this chip in 2009.

The size of the cache on an SSD certainly makes a giant differencethroughput is the main reason Intel’s models have 64MB caches, compared with the 8MB or 16MB cache on a standard hard drive. Still, it seems to me that for anyone building a high-end system with an SSD RAID, or even just a next-gen SSD, SATA 3.0 is mandatory.

Whenever it arrives, that is.