What is network-attached storage?

Network-attached storage is dedicated storage that enables multiple users and devices to retrieve data from centralized disk capacity. The NAS appliance creates a file system on physical media and tracks where file segments are stored. It also maintains metadata for each file -- this might include attributes such as the file name, creation and modification dates and times, size and type.

While file storage is a common use for NAS, some NAS appliances can also support block storage. Block storage has a structure and management system that differs significantly from file storage. Block storage stores data as fixed-size blocks and tends to provide greater performance than file storage, which must allocate some horsepower to the overhead required of its file system.

Block storage is often used for storing the virtual hard disks that are associated with virtual machines. Some databases can also take advantage of block storage.

Benefits of NAS storage

NAS storage offers many benefits for the organizations that choose to adopt it. Some of these benefits include:

• Simple implementation and management. Many NAS appliances offer GUI-based interfaces that largely automate deployment and configuration.
• Simple transition. The move to NAS and its shared storage paradigm is nearly transparent, as the system can continue to work with familiar folder and file formats. That transferability is especially important to small businesses that might not have the IT resources to handle a more technically demanding transition.
• Familiar networking options. All NAS appliances offer Ethernet networking. Organizations with more advanced connectivity requirements will find that many NAS appliances offer a variety of high-speed connectivity options, as well as expansion slots for installing Fibre Channel adapters or other network hardware. 
• Scaling. One of the most appealing aspects of NAS is its ability to scale out to meet increasing capacity demands. Scaling might involve simply adding a new hard disk or solid-state media, hooking in a new shelf of drives, or adding a whole new NAS system and coupling it with the installed NAS through clustering software.
• RAID support. Many modern NAS appliances support a wide range of RAID structures, enabling admins to choose the option that meets their performance and fault-tolerance requirements. Some appliances also enable the installation of hot spares that can be automatically provisioned in the event of a disk failure.
• Supports different media types. Some NAS appliances are designed to support a wide range of media types. A single NAS might for example, offer support for SSD storage, extremely high-capacity HDD storage and even slots for installing NVMe disks. Better still, some NAS vendors enable admins to choose high-speed disks for raw data storage, caching, or both.
• Upgradable. It is often possible to boost a NAS appliance’s performance by installing additional RAM, faster disks or faster network adapters.
• High availability. Many NAS appliances take the concept of high availability beyond the disks that are installed. It is not uncommon for enterprise-grade NAS appliances to feature redundant power supplies and redundant connectivity.

Drawbacks of NAS storage

NAS does have an Achilles' heel or two. Some of the drawbacks associated with NAS storage might include:

• Sprawl. There is a potential for NAS sprawl, which occurs when organizations install a growing number of NAS appliances as a way of keeping up with demand.
• Needed expertise. Unless a NAS appliance is being used for basic file storage, a certain amount of storage expertise is required to configure, manage and maintain the appliance.

What is cloud NAS?

Cloud NAS is an alternative to on-site file storage. Cloud NAS services provide off-site file storage that replaces or augments installed NAS devices. The cost of cloud NAS is generally based on the capacity used and might also include charges for accessing data and for getting data in and out of the cloud service.

Benefits of cloud NAS

• No upfront investment. The main benefit of using cloud NAS is that there is no upfront investment required and no hardware to maintain. Organizations simply pay for the storage and bandwidth that they consume.
• Scalability. Another benefit to cloud NAS is that it is almost infinitely scalable. There is never a need to install additional disks or purchase extra NAS hardware.
• Maintenance. It’s also worth noting that the cloud provider handles all the hardware maintenance. Organizations using cloud NAS will never have to worry about replacing aging hard disks or installing the latest firmware updates.

Drawbacks of cloud NAS

There are some potential disadvantages associated with cloud NAS. Some of these drawbacks include:

• Unpredictable costs. Users are billed for every gigabyte of storage consumed, and most providers also charge customers for data access and data egress. As such, costs can be somewhat unpredictable, and in the long run, the costs likely exceed those of hosting an on-premises NAS appliance.
• Performance. Cloud NAS might not be the best option for storing large, frequently accessed files. Users will notice a significant lag if they try to open a multi-gigabyte file, as the file must be downloaded in order to be used. Users might download copies of frequently used files to their local machines as a way of avoiding the sluggish performance associated with accessing large files in the cloud.

On-site NAS vs. cloud NAS

Choosing between NAS and cloud NAS is context dependent. There are situations in which it makes more sense to use an on-premises NAS appliance. In other situations, cloud NAS is the obvious choice.

Why choose NAS?

On-site NAS represents a one-time expense -- with some recurring costs for maintenance and support. Cloud NAS has monthly charges based on storage consumption. If users buy a 10 TB NAS system, they pay for that capacity once. If users store 10 TB of data in a cloud service, they pay the monthly charge for as long as the data resides in the cloud. So, theoretically, cloud storage could cost more than the same amount of purchased on-site capacity. The same goes for data growth. Expanding capacity with on-site NAS might only involve adding hard disks or SSDs to the existing configuration -- an inexpensive, one-time transaction.

On-site NAS has an advantage over cloud NAS when it comes to data access. System admins can connect a variety of devices and users, as well as create efficient working environments for users who share large files -- such as those used for multimedia.

NAS might also be a good choice for those who are in regulated industries, as it enables organizations to store data securely on premises. Some cloud storage providers also guarantee regulatory compliance, but such a guarantee is not universal.

Why choose cloud NAS?

Cloud storage services have lengthy track records for reliability and data security. They are usually more nimble than on-site resources in dealing with equipment issues or other disruptions. Data stored in a cloud service might be more secure than on-site storage because cloud service providers invest heavily in security.

Cloud NAS has a slight edge over on-site NAS for ease of use -- at least when it comes to setup and ongoing management -- but both are relatively simple to administer and use.

Cloud NAS also has an advantage when it comes to supporting a widely distributed remote workforce. Cloud storage is accessible from anywhere, making it ideal for those who need to share data among geographically separated users.

How to choose the best option for your business

Weighing the pros and cons of on-site and cloud NAS, it's best to start with the following use cases, as they often determine the best fit:

• User file sharing for productivity apps. On-site NAS will likely provide better performance and flexibility for modifications if employees rely on shared files and productivity tools.
• Backup target. On-site or cloud options both work as backup options, but the cloud offers greater resiliency by automatically storing a data copy off site.
• Costs. NAS implementations involve significant upfront costs related to purchasing, installing and configuring the hardware. However, cloud NAS costs are ongoing and will likely cost more in the long run. This is especially true given the hidden costs associated with cloud NAS, which might include data access fees and data egress fees.
• Scalability. Initially, NAS can be scaled by just installing larger disks. Eventually, however, a NAS appliance will reach its storage limit, and the only way to increase storage capacity is to invest in an additional NAS -- or a larger NAS to replace the existing one. Cloud NAS scales on demand without the need for capacity planning or investments in new hardware.
• Data security and compliance. With NAS, the organization has total control over data security. Some cloud NAS providers might offer configurable security settings, but the organization will never have total control over security. Additionally, NAS enables the organization to keep sensitive data in-house.
• Maintenance and overhead. NAS requires IT staff for maintenance and troubleshooting, though the required maintenance is often minimal. Cloud NAS providers handle maintenance on the user's behalf. This reduces the organization’s workload but might increase its dependency on the cloud provider.

Hybrid cloud and other NAS alternatives

One of the most popular alternatives to NAS and cloud NAS is to use a hybrid cloud. A hybrid cloud combines both on-premises and public cloud resources, making it possible to store data where it makes the most sense to do so. An organization might, for example, choose to store its most sensitive data and its large files on premises, while keeping smaller files -- such as documents -- in the public cloud.

Another possible alternative to NAS is to deploy a file server on a physical or virtual machine. Doing so gives the user complete control over the choice of operating systems, hardware and security configuration. The tradeoff for this flexibility, however, is increased costs and complexity.

Brien Posey is a former 22-time Microsoft MVP and a commercial astronaut candidate. In his more than 30 years in IT, he has served as a lead network engineer for the U.S. Department of Defense and a network administrator for some of the largest insurance companies in America.