Not All Hard Drives are Created Equal
A Comparision of Enterprise, Nearline, and Desktop-Class Hard Drives
ENTERPRISE vs. NEARLINE vs. DESKTOP-CLASS HDDs
When it comes to protecting data, a lot of organizations make buying decisions based on cost only instead of selecting the right product for the job. This trend has influenced many popular manufacturers to putting low cost HDDs in their systems. They generate further confusion by focusing on marketing lingo while concealing technical details. Likewise, there’s a certain distrust among some consumers as to whether or not enterprise-class drives are really any better than lower-cost nearline drives. To get past all of this we’ve worked to go beyond the data sheet to get to the bottom line of what makes enterprise-class drives unique and things that should be considered when purchasing drives that only carry a 3 year warranty.
Drive Classes Summarized
Nearline-Class Drives are low-cost, high-capacity intermediate storage solutions that are not needed for high availability transactional processing, and typically do not perform OS or application task, so frequent, rapid access to data is not required. Nearline storage requires 24/7 access for storage/ archiving used for backups or long-term storage with infrequent access to data. They have a moderate MTBF ratio and typical warranties range from 1 to 3 years.
Enterprise-Class Drives have the highest MTBF ratio and are designed for 24 hours/day, 7 days/ week, always accessible. Enterprise systems perform operating system and application tasks locally, and may control multiple drives that add capacity and redundancy to a storage subsystem. During off peak time the enterprise system may patrol hard drives for defects or errors, system backups, and other maintenance tasks. Enterprise workloads create greater wear on bearings, motors, and other components; which generates additional heat and vibration. Enterprise class drives are designed with heavy-duty components and drive firmware programming to meet the rigours of the environment, and utilize sophisticated feedforward anti-vibration circuits to help compensate for vibration. Warranties vary by manufacturer but are regularly up to 5 years.
Each hard drive is composed of about 30 components, depending the size of drive. These items work in concert to deliver a drive that usually lasts beyond it’s warranty. The selection of components and the manner of their assembly are what determine the capabilities of the drive. For the purposes of this piece we’re comparing enterprise, nearline and desktop product lines to better illustrate the differences between each and to highlight where the step up to enterprise drives makes sense.
Rotational Vibration Protection
Figure 1 – RV Sensors Desktop SATA (left), Nearline SATA (center), and Enterprise SAS (right)
By supporting the spindle shaft at both ends, radial response of the disc pack is reduced by 50% compared to a motor which is only supported at the bottom end. A drive with a top cover attached motor will have a substantial advantage in a high vibration environment, like rackmount NAS and SAN arrays, hence the recommendation that enterprise drives be used in larger systems when compared to nearline drives. Also of note are the disk windage plates in the enterprise drive, which reduce air disturbance between the platters for greater reliability.
The bearing systems in the motors have evolved to be very robust. As motor geometry becomes more complex, additional features have been added to the bearings to make them more tolerant of manufacturing variances. The bearings in the motors for enterprise drives are “self purging” which means if bubbles form, they are expelled. They also typically include centrifugal seals which support oil reservoirs giving them an advantage in high temperature environments. Lastly, enterprise drives can support very high pack loads due to relatively high structural rigidity as compared to cantilever style motors.
Voice Coil Magnets(VCM)
High Performance Heads
The table below provides key information needed to help determine hard drive requirements.
Med–7200 rpm - 3.5"
Storage-hungry business applications
Storage Area Networks (SAN) and Network Attached Storage (NAS)
Hyperscale applications/cloud data centers with replicated storage
Substantial scale-out data centers and big data analytics
High-capacity density RAID storage
Mainstream enterprise external storage arrays
Enterprise backup and restore–D2D
Rich media content storage
Reference and compliance data storage
Backup and restore
Desktop or all-in-on PCs
PC-based gaming system
Direct-attached external Stroage Device (DAS)
Network-Attached Storage device (NAS)
High ~12TB (3.5")
Probability of Unrecoverable Errors During RAID Rebuild
Figure 5 – Unrecoverable Error Rate Referenced in Table Above
At the end of the day, the decision on the type of drive to use in anything from a small 2-bay NAS up to rackscale use cases is absolutely critical for data protection and integrity. For small deployments such as home servers, the nearline drive provides enough benefit to the end user that the price delta is minor when compared to the total cost of ownership. In the SMB or enterprise where a rackmount NAS or SAN is in play, the differences are tremendous, using low cost drives is virtually guaranteed to cause problems. At the end of the day, hard drive manufacturers are doing a good job of giving us options based on the intended workload. Enterprise-class drives are clearly superior. Nfina only uses enterprise-class drives in all of our products.