Buying a NAS is not a simple matter of which manufacturer or model only. The most critical aspect of the decision making process has to be the type and quality of the drives used for integration. Select the wrong drives and you can in most cases kiss your data goodbye. Buying a NAS is ultimately for the purpose of making sure data is protected at all times by applying redundancy to a bunch of disks, thus protecting all data. This is only half the story, as a single NAS device cannot be the ultimate backup as many think it is. What happens when multiple drives fail? or disaster strikes and the unit becomes inoperative, the risk of losing data is always a reality. The best protection is to always have a backup of a backup, deploying replication will in most cases drastically reduce the risk of losing all data.
Replication is certainly a serious consideration, however the single most significant factor that determines reliability and continuity falls squarely on selecting the most suitable model and make of hard disk drive. Quite simply the most expensive NAS devices that are packed with features and value for money is totally and utterly use less if you have drives that keep failing or are not compatible with the NAS server. Quite simply select the wrong drives, compatibility and reliability suffers, and so the loss of data becomes reliability.
Our brief is designed to be a comparative guide that will help to better understand the classification of drives based on suitability factors best suited for the selected NAS device.
Hard drive manufacturers develop drives to meet specific customer requirements for reliability, capacity, performance and power consumption. Using drives in the application for which they were designed ensures your data is available when and how you need it. Using drives outside of their intended application can negatively affect the productivity and profitability of your business. A hard drive is a non-volatile storage device which typically stores data on rapidly rotating magnetic platters. Data is usually read/written by a device which is nanometers away from the surface of the platters. Accordingly, vibration can significantly affect hard drive reliability and performance. There are a number of factors that can cause drives to vibrate, including: vibrations from other drives or the drive itself, spindle imbalance/torque, tolerance for rotational input, server capability, population density, and properties of the systems chassis. These vibrations can cause the read/write heads to be knocked off the data track. When this happens, a retry is required to ensure integrity of the read/write data. A retry requires milliseconds of time, however, because drive and storage subsystem electronics are operating in micro or nanoseconds, a wait of milliseconds significantly reduces the overall performance of the storage solution.
Two general categories of drives have evolved to meet customers’ needs:
Desktop drives perform at an acceptable level when rotational vibration does not exceed 10 radians per second. Desktop drives are typically used in single or dual – drive environments where rotational vibration is limited. A desktop drive is built to have typical reads or writes 50 to 80 times a day over an 8-hour period, 5 days a week. Desktop drives are designed to work in environments that do not exceed 25 degrees Celsius. As heat increase, the MTBF decreases and the drives are more likely to fail. These drives may be suitable for entry level NAS servers mainly used as secondary or archive purposes, but not for primary or mission critical storage deployment.
Enterprise drives perform at an acceptable level when rotational vibration does not exceed 21 radians per second. Enterprise drives are typically used in multi-drive environments where rotational vibration is normally above 10 radians per second. Enterprise drives are built using more advanced technology and components to meet the performance, workload, and reliability needs to perform hundreds of thousands of read/writes per second, 24 hours a day, 7 days a week. Enterprise drives are also designed for higher temperatures. The low end of their temperature specification is at the high end of the desktop specification, making enterprise drives highly reliable in applications where desktop drives fail. Enterprise drives usually have a longer warranty period than desktop drives. Enterprise drives often have advanced power management. These modes reduce power consumption along with server cooling requirements, both of which equate to lower operational costs and less thermal impact on surrounding system components. Enterprise drives with error recovery control have the ability to quickly respond with data or return an error to the host controller. With a quick response the RAID set is preserved through rebuilding of requested data. Full RAID set rebuilds are only executed for true drive failures. To lower costs on desktop drives, error recovery is not a common feature. A desktop drive in a similar situation would respond too slow to preserve the RAID and the drive is flagged for replacement. The RAID set would operate in a slower degraded mode until the drive was replaced. Complete loss of data is possible if another drive times out during the degraded mode. With higher MTBF and error recovery, enterprise level drives offer greater reliability than desktop drives in the server environment. The Enterprise drives are best suited for mission critical primary storage and can be integrated in any other NAS server environment if needed. Alternative to SATA drives are the new SAS drives that are designed for high end storage and servers to perform at optimum levels.
Hard drives last longer when used in the application for which they were designed. Desktop drives often lack workload management to lower thermal stresses; have a lower tolerance for the normal rotational vibration found in a raid based storage environment; are not designed to run twenty four hours a day, seven days a week; and may fail prematurely when installed in a NAS server. To get the best performance and avoid drive failures we strongly recommend using enterprise drives for NAS servers for mission critical data.