Driven by an insatiable thirst for more storage capacity, the capabilities of network attached storage (NAS) appliances have been improving by leaps and bounds. Their prices have also fallen substantially, with a basic two-bay NAS chassis available for as little as a couple of hundred dollars\u2014a far cry from the thousands they used to cost. Their affordability represents a huge opportunity for small and mid-sized businesses (SMB), which now find it possible to host multiple terabytes of data on their network at a fraction of the cost of a traditional file server or storage area network (SAN).\n\nSo what should SMBs be on the lookout for when shopping for a NAS? We've put together a list of the most desirable features below, grouped into several broad categories. You may not need everything mentioned, though it is hoped that this will help you arrive at a decision about the right NAS for your organization.\n\nNAS HardwareWhen buying a new NAS systems, the first question will obviously be centered on the projected storage capacity that will be required, which is closely related to the number of supported hard disk drives (HDD). Note that some NAS options may be upgradable with an expansion chassis for additional drive bays. Also, be on the lookout for support of external storage devices using USB or eSATA ports, which may be useful as a temporary capacity fix, or for the purpose of performing a backup. (See "Data Backup and Synchronization" below.)\n\nDo remember to ensure that the NAS is capable of supporting the largest capacity HDD currently available, which would be 3TB for a 3.5-inch SATA HDD at the time of writing. Some NAS appliances are compatible with both 3.5-inch and 2.5-inch form factors, though the latter may be of limited utility unless there are plans to deploy solid state drives (SSD). HDD should also be hot swappable for maximum flexibility, though today only the most basic models NAS do not support this feature.\n\nIn terms of network connectivity, the common denominator at the moment appears to be gigabit Ethernet, though dual gigabit Ethernet ports are increasingly common in mid-range NAS models. However, do not assume that link aggregation is automatic with units with dual Ethernet ports, as some work only in fail-over mode. Some NAS may also be upgradable to 10G Ethernet with an add-on card, which may be an important consideration if there are plans eventually to upgrade the core network to 10G networking.\n\nIt is also important for businesses to consider whether the NAS comes with a redundant power supply unit (PSU). Failure of individual drives aside, the PSU is the hardware component most likely to experience a critical failure, and depending on the immediate availability of spare parts, that failure can result in a lengthy downtime. \n\nHard Disk PerformanceTransfer speed over the network is the primary performance indicator of a NAS. This transfer speed is typically measured when uploading or downloading large files from the appliance using a file-level protocol, and where applicable, at the block level as well. The importance of each will of course depend on the anticipated usage of the NAS\u2014a better file access speed is key for businesses looking to deploy the NAS as a storage repository for users, while a good block access speed is of interest to outfits intending to deploy it with servers.\n\nSome high-end NAS may support auto-tiering with SSD for enhanced performance, though the exact performance boast here is not easily evaluated. Given that most mid-level NAS systems sold today are already capable of saturating a gigabit connection, it is advisable to avoid placing undue emphasis on absolute performance figures. Unless the performance is particularly bad, businesses should evaluate the performance traits of a particular NAS together with its overall capabilities.\n\nFile Storage CapabilitiesIn terms of file-storage capabilities, you may expect the prominent NAS brands all to support major file-transfer protocols such as CIFS, NFS, AFP (Mac OS) and even FTP. More advanced NAS will also support iSCSI for block-level storage over the local area network. The ability to perform thin provisioning is a related capability that facilitates the creation of volumes larger than the available physical space, and is of use when deploying a block-level storage volume. Finally, if a NAS can communicate with an uninterruptible power supply, it can significantly reduce the risk of disk corruption by facilitating a safe shutdown in the event of an extended power outage.\n\nNon-Core NAS CapabilitiesTo stand out in this highly competitive field, NAS makers have started incorporating a litany of non-core capabilities into their storage appliances. These range from basic features such as the ability to send out an email notification upon certain system events to higher-end capabilities such as native Time Machine support.\n\nOther common non-core capabilities include network services not related to storage, such as support for a print server, NTP server and Syslog server. Some vendors even offer mobile apps for the remote monitoring of the NAS from a smartphone or tablet, which may include the ability to tweak certain simple parameters. While these kinds of additional features are always good to have, be careful not to let them distract from the key criteria necessary for your SMB.\n\nSecurity and User ManagementSome higher-end NAS models may incorporate the capability to encrypt hard disk drive data. Encryption is a definite plus, especially if the systems are to be deployed in locations such as branch offices where it is difficult or impossible to secure the NAS. It is important to note, however, that unless a NAS incorporates dedicated encryption hardware, enabling encryption invariably has a huge negative impact on the write performance of the NAS. Moreover, the use of encryption may also slow down the time required to rebuild a failed HDD.\n\nUser management, which pertains to the ease in which user accounts are managed, and usually extends to the creation of groups, is a feature closely related to security. Mid-sized businesses will probably require support for Active Directory or LDAP, while SOHOs and small businesses may be satisfied with more rudimentary controls. Because clunky or buggy user management tools can be a deal breaker for large organizations, it may be prudent to request an evaluation unit in such scenarios. In the process, be sure to check for the maximum number of user accounts or shared folders that are supported and verify that they are adequate to meet the needs of your SMB.\n\nData Backup and SynchronizationTo address the need for backups, some NAS products may come with the capability to perform a data backup onto an external storage medium or over the network. The most basic approach is through an external storage drive connected via USB or eSATA. For organizations that generate low volumes of highly critical data, batch jobs can be used make regular backups of these data as a safeguard against accidental deletion or\u2014if a ruggedized hard disk drive such as the ioSafe SoloPRO External is used\u2014from a localized disaster such as a fire or a flood.\n\nThe synchronization of data between two NAS appliances across the network is a more advanced feature that is currently gaining traction. For example, Iomega claims that the recently announced StorCenter ix2 NAS supports easy-to-set-up, device-to-device data replication over the network. This essentially allows SMBs to create a private cloud by deploying two NAS appliances at different locations. Of course, the actual feasibility of a replication across a WAN will vary depending on a number of factors, including its importance to the individual business, the amount of data to be replicated and the cost of bandwidth. Nevertheless, it offers a glimpse of a capability that was once in the sole domain of the most expensive SANs.\n\nFinally, NAS vendors have also started adding support for online storage services, with mature cloud services such as Amazon S3 being the most commonly supported platforms. As with everything stored in the cloud, the onus is on individual businesses to exercise the appropriate caution to ensure that all uploaded data are encrypted. Given the fickleness of an Internet connection, cloud storage should never be the sole backup target due to the potential inability to meet the recovery time objective when attempting a disaster recovery.\n\nIP Camera SupportWhile an IP camera is not a major capability by itself, some NAS vendors have started incorporating support for the feature into their appliances. Given its ample storage capacity, the NAS is indeed ideally suited for storing the large amount of data generated by a typical network-attached camera. Do note that features such as the actual supported frame rate, camera count and maximum supported resolution can vary widely across NAS brands or even models. Similar variations are found in related capabilities such as camera management and the ease with which captured video footage can be reviewed. If support for a particular model of IP camera is important, make sure to discuss it directly with the vendor prior to making a purchase. Note that additional licensing costs may apply for each IP camera.\n\nSoftware UpgradesBusinesses are unlikely to select a NAS based on the possibility of future software upgrades. Given the complexity of the modern NAS appliance, however, it may be reassuring to know if a vendor has a track record of releasing security patches to resolve the inevitable bugs, or even occasional feature updates. Fortunately, this can be determined relatively quickly by visiting a vendor's website and checking out its product support page. Indeed, some NAS vendors such as Synology have been known to release regular and fairly significant updates\u2014at no cost.\n\n\nPaul Mah is a freelance writer and blogger who lives in Singapore. You can reach Paul at email@example.com and follow him on Twitter at @paulmah.