Reason #2: Other Performance Factors
There’s More To An Enterprise Drive
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Of the three classes of hard drives—desktop, nearline, and mission critical—each is classified to exhibit a certain amount of performance impairment at given RV levels. Desktop drives begin to demonstrate throughput loss at nearly the first sign of vibration. They fall to 80% performance at just 6 rads/sec2. Nearline drives, such as Seagate’s Constellation ES.2, can take just over twice as much vibration before meeting that same 80% performance threshold. However, top-end enterprise mission critical drives, such as the Seagate Savvio15K family, can withstand 28 rads/sec2 before any performance decline sets in. This reflects the impressive amount of RV control technologies at work within the drive.
You can see the effect of external vibration on drive performance shown in 2005 testing done by I/O Performance’s Thomas Ruwart and the University of Minnesota’s Yingpang Lu (see www.dtc.umn.edu/publications/reports/2005_08.pdf). Their data clearly shows how vibration causes significant numbers of performance drops in a Maxtor consumer drive. Note the three-second period in which vibration was suspended, just to illustrate the point. In contrast, the Seagate Constellation ES enterprise drive, which employed RV tolerance technologies, showed essentially no negative effects from the vibration.
A subsequent study in 2010 by Julian Turner of Q Associates (see http://static.usenix.org/event/sustainit10/tech/full_papers/turner.pdf) investigated the impact of RV on a 16-disk Sun 7110 array running in a modern data center environment. Turner found that “random reads and writes are significantly impacted by vibration in the data center environment. Performance improvements for random reads ranged from 56% to 246% while improvements for random writes ranged from 34% to 88% for a defined set of industry benchmarks.” In other words, when performance equals money, an organization may only be getting half of its money’s worth from storage subsystems unless drives are employing RV-tolerant technologies.
Note that sensors and feedback/feed forward mechanisms are not the only path to RV dampening and performance gain. Seagate employs many methods, some of which involve firmware-based seek profiles to minimize torque. The company also employs a Top-Cover-Attach spindle motor design that increases rigidity, and thus dampens vibrational leeway, within a four-platter drive. You can see in the Seagate-provided charts here the impact of a top-cover attached motor on lowering in-cabinet disturbances caused by internal motor frequencies.
Reason #2: Other Performance Factors
Yet, there’s more to an enterprise drive than just its higher RV tolerance. To begin with, users must determine the spindle rotation rate appropriate to their throughput needs. As in the OpenDNS example above, drives using a 7200 RPM rate, such as the Constellation ES.2, offered an appropriate balance between moderate peak speed, high capacity, top reliability, and low price. Applications demanding higher speeds will gravitate to 10,000 RPM or 15,000 RPM drives, or even take the jump into SSDs if capacity and cost is less of a concern.

Next is the distinction between SATA and Serial-attached SCSI (SAS) interfaces. As the modern evolution of old school parallel ATA technology, SATA started out and remains a predominantly consumer-centric technology. That said, a sizable chunk of the enterprise market now uses SATA for high-capacity, low-throughput, low-cost applications, such as archival storage. The SATA interface, currently topping out at 6 Gb/s, offers no speed advantage over SAS in itself, but because SAS technology is natively dual-ported with multiple channels per drive, those channels can be bonded for higher aggregate performance. For example, a “x4 wide port” might combine four 3 Gb/s channels to provide 12 Gb/s of total bandwidth. (Whether the heads can pull anything close to that much data from the platters is a different issue.) The two ports found on most SAS drives are used less for aggregate performance and more for reliability. If one port or connection fails, the drive can automatically switch to using the other port.