Market Overview
Business demand on storage is increasing and the challenge to effectively control the way that vast amounts of data are created, stored, and accessed is intensifying as a result. To address data growth without interrupting business operations, the ability to rapidly deploy storage and IT resources to meet that increasing demand becomes a function of scalability. The primary objective of any type of scaling is therefore to create a dynamic, non-disruptive environment that supports data growth in such a way that system capabilities remain as balanced as possible.
Scale-up Introduced
To support growth, putting it very simply, infrastructure capabilities can be added to the current devices (scale-up) or more devices can be added into the environment (scale-out). For many IT users, scaling up their existing storage infrastructure to much faster storage devices, or even higher-performance computing platforms, can meet their needs perfectly adequately when compared to expanding infrastructure by adding more nodes or moving to more complex cluster or grid topologies. Storage resources continue to get faster, become cheaper, and offer larger capacities, which increases the appeal for both scale-up and scale-out architectures. Scale-up solutions let users increase compute power, add storage (performance or capacity), or create more network ports by implementing bigger and faster (often proprietary) resources rather than adding more (often commodity) resources.
Scale-up Analysis
Scaling up (vertical scaling) is accomplished by replacing or upgrading existing components with more powerful resources; as such, it can be applied to all major elements of computing infrastructure—leading to, for example, faster servers, higher capacity storage devices, or switches with higher port counts. Scaling up has historically been most tightly associated with regard to servers, though any IT resource can be scaled up or upgraded to a newer faster model. A server can be scaled up by upgrading from several small servers to a larger, high performance or multi-core server to increase overall compute power and reduce the number of management touch points.
Scaling storage up can be done by making existing storage nodes in a system larger and/or faster and/or more powerful. A scale-up storage example could be adding higher capacity storage devices to replace older, lower capacity devices in order to increase the overall capacity of the storage pool. Replacing a HDD (hard disk drive) with a faster flash-based drive or a solid state disk is another example of scaling storage up—in this case, to improve IO performance.
In the simplest terms, scale-up storage usually means either adding more to the existing storage and/or consolidating several smaller devices into a larger device, thus reducing touch points and simplifying management efforts. Fewer devices usually also mean less floor space and less energy consumed. A consideration for scale-up architectures is that they can’t span multiple locations or easily scale beyond the maximum capacity of any single storage node. Another consideration with scaling up is the potential lack of overall resiliency (without specialized constructs to add this) compared to the added redundancy that scale-out architectures more typically and easily provide.
Scaling Storage Topologies
Although scale-up is often assumed to be synonymous with SANs and scale-out, in turn, is assumed to be synonymous with NAS, the truth is that scaling is not a direct function of the storage type; scale-up can therefore apply to all three major storage topologies:
DAS: As the first widely popular storage model, DAS (direct attached storage) implementations still comprise a large proportion of the storage capacity on all major operating systems. It is simpler to manage and can scale up for added performance and capacity by adding larger control units and faster drives or cascading additional control units; however, DAS doesn’t provide many of the efficiencies and advanced functionalities that simplify management efforts and add operational advantages as the storage pool increases.
NAS: Network attached storage (NAS) is a special purpose device comprised of servers, disks, and management software dedicated to serving files over a network. Scale-up NAS can be associated with adding larger and faster—as opposed to more—NAS nodes that allow capacity and performance to scale as needed.
SAN: Scaling up is also an important aspect of SANs (storage area networks) and is often used to consolidate smaller SAN “islands” with individual switches into larger, single fabrics or it uses routers to physically connect the switches while logically isolating the fabrics. By offloading many traditional storage management functions from the host, SANs provide an effective scale-up capability for large enterprises that anticipate significant storage growth. Unlike DAS, excess capacity in SANs can be pooled and more easily shared, resulting in higher utilization of resources.
Making a Choice
The key for any organization selecting an optimum solution is to understand which of its goals are most important. Table 1 is a quick summary guide of the factors to consider in terms of topologies and scaling, although the eventual decision will also need to take other factors (such as functionality, price, TCO, and skill/comfort levels) into account.
The Bigger Truth
Scale-up and scale-out are both valuable storage tools and many organizations will continue to employ both for the foreseeable future as both have useful, though varying, attributes. For example, scaling up an existing system can often keep storage management simpler as compared to scale-out storage as the complexity of the underlying environment is reduced. That said, scale-up storage systems can only scale as far the performance and capacity limits of the individual storage resources permit. Conversely, a well implemented scale-up storage model (whether SAN, NAS, or DAS) can provide very timely provisioning, often with greater resource utilization, and deliver known levels of data and system availability. Perhaps it is best to consider the two approaches in combination; what is certain is that scaling up and out will continue to play ever larger roles in IT as demands to service business growth in a flexible manner climb ever higher.
