Drive Types, Cont.
Seagate vs. WD: Battle for the SOHO NAS Crown
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Another problem with traditional consumer hard drives is their susceptibility to vibration. Because the motor in a hard drive is a spinning piece of machinery, it emits some amount of rotational vibration (RV). At the same time, the read/write head on a hard drive must be able to interact precisely with infinitesimal magnetic particles on spinning platters in the presence of this vibration. This becomes significantly harder if there are multiple hard drives in a single cage (whether it be a four-bay NAS box or an 8U racked storage server), all of which emit vibration to one another. Then add on more vibration emitting from fans and any other moving parts within the system. These factors can contribute to so much RV rattling a drive that it can no longer efficiently read/write data.
Consumer drives tend to be more susceptible to RV-induced errors, in part because of how their motors are built. Extra precautions are built into Seagate Enterprise Capacity HDDs (formerly Constellation ES.3) — for example, using a motor that is attached to both the top and bottom drive covers. This better balances the drive, dampens vibrations, and improves performance in single- to five-drive environments. Drives aimed more at large-scale storage arrays, such as the Seagate Terascale HDD line, tend to use additional technologies, such as RV sensors, that can help drives better cope with external vibration forces.
Enterprise drives are designed with a higher level of error recovery controls. Read/write errors happen eventually, even to the best drives, but desktop hard drives will be more prone to falling out of RAIDs and thus triggering a lengthy, resource-swamping array rebuild process. (Note that some RAIDs may be more prone to unrecoverable data loss when arrays are in the process of rebuilding.) When a drive suffers a read/write data error, it issues a recovery request to rebuild that data. RAIDs are often designed to drop faulty drives in seven seconds and then commence a rebuild. However, desktop drives can take 20 seconds or longer for data recovery. Business-optimized drives can take steps to avoid this. NASWorks tied to the NAS HDD, for instance, will detect a data error and request help from the RAID to rebuild it. Because the RAID houses an older copy of the data, the RAID can supply the needed backup bits and circumvent the need for a rebuild.

Manufacturers also try to distinguish their drive lines by feature set. In the chart on page 2, you’ll notice that the Terascale HDD features Instant Secure Erase (ISE) while the NAS HDD does not. (Seagate’s 3.5-inch consumer drives lack this feature, as well.) The ISE feature lets a user or remote administrator issue a command that deletes the drive’s cryptographic key, essentially cryptographically wiping the drive in a matter of seconds. The need for this sort of feature generally doesn’t crop up until one gets into deployments larger than a four- or five-bay NAS appliance.