Chipset-level support for NCQ has been around since Intel launched its 900-series chipsets this summer. NVIDIA's new nForce4 chipset also supports Native Command Queuing, as does SiS's latest south bridge chip. Hard drives that support NCQ are also trickling into the market and Seagate has been shipping an NCQ-equipped version of its popular Barracuda 7200.7 Serial ATA hard drive for some time. We've snagged a 'cuda 7200.7 NCQ and run it through an exhaustive suite of benchmarks, putting NCQ to the test against not only queue-less Serial ATA drives, but also a Western Digital Raptor that supports Tagged Command Queuing (TCQ). Read on for more on what command queuing is all about, where it helps performance, and where it might actually slow you down.
Native Command Queuing explained
Since support for Native Command Queuing (NCQ) distinguishes the Barracuda 7200.7 NCQ from its predecessor, it's worth taking a moment to examine what NCQ is and where it might improve performance. Hard drives read and write bits to a spinning platter, but the drive head spends most of its time idling as it waits for the platter to spin to the appropriate position for a given read or write operation. This delay is referred to as a drive's rotational latency. For typical 7,200-RPM desktop drives, rotational latencies are over four milliseconds. That's less than the blink of an eye, but in the lightning-quick confines of a computer system, it's a virtual eternity.
The most obvious way to reduce rotational latency would be to spin a drive's platters faster. If the platter is spinning faster, the drive head will spend less time waiting, and performance should improve. SCSI drives that spin at 10,000 and 15,000-RPM typically boast three and two millisecond rotational latencies, so spindle speed certainly makes a difference. However, getting platters to spin at higher speeds is ultimately a brute force solution to the rotational latency problem. Getting platters to reliably spin at 10K and 15K-RPM isn't a mechanically trivial task, either.
Rather than relying on faster spindle speeds to reduce rotational latency, Native Command Queuing aims to minimize the performance impact of a hard drive's mechanical latency by intelligently re-ordering I/O requests. Normally, a hard drive blindly executes I/O requests in the order that they are received. NCQ allows a drive to gather multiple I/O requests and reschedule them based on their proximity to the drive head's position.
In the above example, a normal hard drive would take two rotations to execute I/O requests one through four in order. With NCQ intelligently optimizing the request order, the drive can execute all four requests in only one rotation, saving precious milliseconds.
Of course, the above example is a best case scenario for Native Command Queuing. NCQ can only improve performance when I/O requests reference different physical locations on a disk, so it can't do much for streaming drive loads unless a drive is heavily fragmented. Native Command Queuing is perhaps best suited for multitasking and multi-user environments with more random I/O profiles. In fact, command queuing is so effective in multi-user environments that SCSI drives have been using it for ages.
Command queuing may be old hat for SCSI drives, but it's new for Serial ATA. It's not the only Serial ATA command queuing scheme, either. Western Digital's Raptor WD740GD supports Tagged Command Queuing (TCQ), a variation of command queuing that's similar to NCQ. Thus far, the WD740GD is the only hard drive to support TCQ, and with NCQ a part of the Serial ATA II spec, it seems unlikely that other SATA drive manufacturers will adopt TCQ. SATA-II isn't required to support NCQ, though.
The Barracuda 7200.7 NCQ is a new spin of Seagate's existing 7200.7 technology. Other than the addition of NCQ support, the two drives are quite similar.
|Barracuda 7200.7 NCQ||Barracuda 7200.7|
|Maximum external transfer rate||150MB/sec|
|Maximum sustained transfer rate||58MB/s|
|Average seek time||8.5ms|
|Average rotational latency||4.16ms|
|Available capacities||80, 120, 160GB||80, 120, 160, 200GB|
|Idle acoustics||2.5 bels|
|Idle power consumption||9-9.3W||9W|
|Seek power consumption||12.5-13.5W||13.5W|
|Warranty length||Five years|
With similar names and specs, picking an NCQ-equipped 'cuda out of a crowd might be a little difficult. Barracuda 7200.7 NCQ drives can be identified by their model numbers, ST380817AS, ST3120827AS, and ST3160827AS for 80, 120, and 160GB drives. Unfortunately, Seagate doesn't offer a 200GB 7200.7 with NCQ support.
The Barracuda 7200.7's specs haven't changed much for the NCQ spin of the drive and neither has Seagate's five-year warranty. Five-year warranties are usually reserved for high-end SCSI drives and enterprise-class 10K-RPM Serial ATA drives, so Seagate should be commended for serving up five years of coverage for its 7,200RPM Barracudas. However, it should be noted that Seagate's five-year warranty only applies to retail-boxed and bare drives sold through authorized resellers. For drives sold directly to OEMs for integration in their systems, warranty coverage is up to the OEM. That's standard industry practice.
Hard drives aren't usually much to look at and the Barracuda 7200.7 NCQ is no exception. Here are a few shots of the drive anyway.