Features and Design
Nearline vs. Desktop: Deploying Value in the Data CenterSince enterprise drives are built for data centers, environmental tolerance plays a key role in drive design. Chief among environmental concerns is vibration. In a desktop system, there are probably a few fans and perhaps one or two other hard drives creating rotational vibration (RV). All spinning motors give off some amount of RV, but, as one might recall from high school physics, vibrations are waveforms, and waves can be additive. The more RV sources there are in a closed system, the more the system will be prone to periodic RV spikes as vibration crests overlap. Put plainly, if one has a bunch of drives in a case, that case may be prone to some extreme vibration, and that vibration can impact a drive’s performance.

Source: Seagate
A solid enterprise drive, such as the Seagate Constellation ES drive, can withstand 12.5 rad/sec2 of RV without experiencing any performance impact. Meanwhile, a desktop drive loses nearly half of its performance at this vibration level. And it goes almost without saying that desktop drives will be more prone to damage and premature failure than an enterprise equivalent in the face of prolonged, substantial vibration. Having more robust chassis and enclosures can help mitigate this problem, although with higher-end cases obviously come higher-end costs.
Several design factors contribute to the enterprise drive’s robustness here. For instance, modern nearline drives have top cover-attached rather than bottom-mounted spindles. This tends to make the drive more rigid and better able to resist vibration. In addition, drives such as the Constellation ES.3 drive integrate RV and linear vibration sensors. These sensors allow the drive to compensate for vibration originating either within or external to the drive. Differences also exist in the drive firmware, which can control different seek profiles and thus minimize the impact of the vibration.

Beyond physical design elements suited to data centers, enterprise drives usually host a range of data center-suited features. At present, both desktop and enterprise drives feature 6Gb/s interfaces, but only enterprise drives have Serial-Attached SCSI (SAS) options. Whereas SATA is a half-duplex technology, meaning that it can only communicate with the host system in one direction at a time (walkie-talkie fashion), SAS drives can communicate in full-duplex using two ports (like a telephone), allowing for much faster request processing. SAS drives have much greater queue depths, which help them to handle commands from multiple users far more efficiently. While SATA will remain at 6Gb/s for the foreseeable future, SAS is now en route to 12Gb/s and beyond. Not least of all, SAS features more robust error detection and correction capabilities — a must in business environments. Note that nearline drives feature additional error recovery features not found in desktop drives. This is particularly critical in RAID situations where double drive failure can mean irretrievable data loss.

Some nearline enterprise drives, including the Constellation ES drive, offer self-encrypting models (SED). These feature integrated cryptographic processors able to safeguard all drive contents with government-standard AES encryption. While individual systems can employ this encryption, enterprises wanting to manage fleets of encrypted systems will need third-party software tools for key management. This allows IT managers not only to keep much tighter control over their data assets but also to employ the drive’s cryptographic Seagate Instant Secure Erase (ISE) feature. Whereas traditional hard drive disposal or repurposing requires time-intensive and costly erasure methods, ISE allows IT to securely wipe a drive in seconds with little more than a mouse click.
In the same vein, a select number of enterprise drives have passed the stringent requirements for FIPS 140-2 certification. The United States and Canadian governments both require their agencies and any associated contractors to use FIPS 140-2-approved storage devices when handling sensitive data. These drives, which include the Seagate Constellation ES.3 drive, feature security features above and beyond even the most robust 256-bit AES encryption.
Finally, bringing us full circle, while enterprise hard drive spec sheets may note higher power consumption levels, mature drive designs will employ user-configurable power-saving schemes, such as Seagate PowerChoice™ technology. Based on industry-standard power management approaches from the T10 and T13 storage standards bodies, PowerChoice technology adds new functionality on top of Seagate prior-generation features. PowerChoice technology allows the host to tune motor and electrionics settings for optimal power savings. According to Seagate, PowerChoice technology can lower drive energy consumption by over 50% in data center environments.
By now, it should be clear that the price difference between Seagate desktop and nearline models is not the gating factor it might seem at first. Yes, adopting enterprise-class drives over their desktop counterparts will necessitate higher up-front spending. However, the subsequent benefits in higher performance, potentially lower power consumption, lower risk of data loss, and lower maintenance and replacement costs will make up this price difference many times over.
