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Serial ATA and SATA RAID advances represent more big changes in the world of postproduction.

Serial ATA hard drives and SATA RAID solutions may be the hottest new storage technologies in the last decade. The Serial ATA interface, which replaces the parallel ATA interface, provides improved performance, longer cable connections, and advanced features for integration into servers and networked storage. In short, it represents a major shift in storage technology.

In the 1980s, PC technology companies formed an association to develop standards for the IDE interface called the Advanced Technology Attachment Standard or ATA. This parallel-connection standard became the near-universal storage interface protocol for personal computers — both desktops and laptops. A major reason for such popularity is that IDE hard drive solutions are less expensive than SCSI hard drive solutions.

This association continued to improve the performance of the interface standard. The group developed the Enhanced Integrated Drive Electronics (EIDE) specifications and the Advanced Technology Attachment Packet Interface (ATAPI) to support devices such as CD-ROM, DVD-ROM, and recording optical drives. Many other specifications evolved, including those dealing with: protecting data, more reliable data integrity, multiple data transfer modes, and more recently, the Direct Memory Access (DMA) and Ultra DMA standards.

But there are limitations with the parallel IDE or ATA interface. The limitations of an 18in. cable, the 40-pin connectors of the ribbon cables, and the 5V signaling requirement all caused the PC companies to seek an alternative.

A Serial ATA working group (www.serialata.org) was formed, and the Serial Advanced Technology Attachment (SATA) interface for hard drives and the Serial ATAPI interface for ATAPI devices were established. These specifications eliminated many of the problems. For example, the parallel ribbon cable has been replaced by a serial cable that can be up to a meter long. This gives greater flexibility in routing the cable in the computer chassis and improves airflow. The specification also calls for a low-voltage requirement (500 millivolts), and error-checking and correction capabilities.

The Serial ATA working group has recently introduced the SATA II specification extensions. These extensions include a 300MBps data transfer rate — compared to the 150MBps transfer rate of the original SATA specification, or the 133MBps of the current IDE specification. Further improvements, including data rates of 600MBps, are expected shortly. Other changes will include letting users connect a single host to many SATA drives, and allowing two different hosts to connect to a device, which gives the ability to offer fully redundant servers and backup solutions. SATA II products are now being displayed at trade shows by a variety of manufacturers.

SATA hard drives have been available with bridge solutions, but native SATA drives are just now coming to market. Manufacturers include Seagate, Maxtor, Hitachi, and Western Digital. It is expected that the low-cost SATA hard drives compatible with SATA II extensions will replace the legacy hard drives in most personal computers beginning in 2004. It should be emphasized that the SATA II extensions do not change the SATA 1.0 hard drive specification.

For the desktop video content creator, a major benefit of all this is that these low-cost hard drives can be put into RAID configurations for better hard disk performance. When multiple disks work at the same time, your read/write speed is considerably better than when using a single hard disk.

The performance of a SATA-based RAID solution is comparable to the traditional SCSI RAID solutions costing twice as much. For example, ProMax offers a two-drive internal SATA (500GB) for the Mac for $1,195.

This particular ProMax solution uses the software-based RAID capabilities of today's Apple OS X operating system, which is capable of striping two RAID hard drives. (Note: This solution includes a FireWire 800 drive for the operating system and applications.) Microsoft's Windows Operating system, together with Intel- and AMD-based mother-boards, may also offer a RAID capability.

For larger RAID configurations, low-cost SATA RAID controller cards are available. The RAID controller frequently contains a large memory cache that dramatically increases performance. The leaders in this new card technology are 3Ware and Promise Technology, although Adaptec, Intel, and many others are offering such cards.

3Ware's Escalade series can connect 12 hard drives for 3TB of RAID stor-age. Promise Technology offers hot-swappable drive enclosures and its FastTrack cards, featuring four SATA ports with 1.5Gbps per channel.

This technology is scaleable as well. 1Beyond offers SATA RAID workgroup solutions up to 3.5TB (270 hours of DV or 54 hours of SD uncompressed). Rorke Data offers the Galaxy 16i SATA RAID solution, capable of 4TBs in a 3 RU space. These are just examples of a growing range of solutions.

As with all new technologies, there will be growing pains, but Serial ATA technology and SATA RAID solutions are here today and will dominate in the near future. With a SATA II RAID solution, DV, uncompressed standard definition, and (conditionally) even high-definition video editing can be accomplished.

In my last column, I told readers about my investigation of the latest low-cost, software-only applications for today's personal computers. I plan to put one or more SATA II solutions to the test also. If you would like to comment or have a question, I can be reached at bob.turner3@comcast.net.

Sidebar
A brief look at RAID levels

THE GOAL OF RAID (REDUNDANT Array of Independent [or Inexpensive] Disks) is to combine multiple inexpensive disk drives to obtain performance, capacity, and/or reliability that exceeds that of a single large drive. The host computer sees this drive array as a single logical drive.

The process of combining these arrayed drives to appear as a single storage device is called striping. When you stripe an array of drives, you are assigning the array to store data in a sequential process where the flow of data is interleaved in a balanced manner. This interleaving can greatly improve data access speeds and throughput.

There are several types of RAID striping, known as levels of RAID. These levels of RAID allow you to achieve performance at one end of the spectrum, and redundant protection at the other.

RAID Level 0 offers the highest performance, with data broken down into blocks and written simultaneously on each drive in the array. Since the input and output loads are spread out over multiple drives, storage performance and throughput can greatly improve. Generally, having more drives in the array and spreading the load over multiple arrays can increase performance. On the other hand, there is no redundancy. If one drive fails, you have lost all of your data. There is no recovery process.

RAID Level 1 mirrors pairs of drives. This means that in a drive pair, the second drive is a duplicate of the first. If one drive fails, all of your data is still there on the second drive. The price you pay for this protection is the cost of a drive pair (versus a single drive for the same amount of data stored) and the slight performance hit of recording identical data on to two drives at the same time. If a drive should fail, you replace the drive and the replacement drive is rebuilt with a re-mirroring process. In some Level 1 solutions, there is a “hot spare” so this re-mirroring process can be automated.

RAID Level 3 is similar to Level 0, but reserves a dedicated disk for recording parity data. This provides for a limited amount of fault-tolerance. This solution features high read and write data rates, so it is still used in video environments, especially for single computer storage as opposed to workgroup solutions. But it requires synchronized-spindle drives to avoid performance degradation, and the controller design is considered complex — it may be too complex for software-based RAID control.

RAID Level 5 stripes data and parity information across the entire array's drives in a sequential manner. This solution is sometimes referred to as a “rotating parity array.” If one drive in the array should fail, the lost data can be computed and recovered. This solution requires a minimum of three drives in an array. It offers a performance compromise, as the read performance is excellent, but the write performance is considered medium at best. Also, recovery time is required should a drive be lost. You must remove the lost drive from the array and the data is re-calculated and re-built on the replacement drive.

Some Level 5 RAID solutions have what is known as a “hot spare,” and this rebuilding process can happen automatically on the spare drive. Level 5 is quite popular for general purpose computing because it combines efficient, fault-tolerant data storage with good read performance.

There are several other RAID levels, but they are not common, no longer available, or available only from a single vendor. Also, they may be extraordinarily expensive.
— BT