Companies are always on the lookout for simpler, most cost-effective methods to manage their infrastructure. This explains, in part, the emergence of scale-out architectures over the last few years as a preferred means for implementing backup appliances. It is as scale-out architectures gain momentum that it behooves companies taking a closer look at the benefits and drawbacks of both scale-out and scale-up architectures to make the best choice for their environment.
Backup appliances primarily ship in two architectures: scale-out and scale-up. A scale-out architecture is comprised of nodes that are logically grouped together using software that the vendor provides. Each node ships with preconfigured amounts of memory, compute, network ports, and storage capacity. The maximum raw capacities of backup appliances from about a few dozen terabytes to nearly twelve petabytes.
In contract, a scale-up architecture places a controller with compute, memory and network ports in front of storage shelves. A storage shelf may be internal or external to the appliance. Each storage shelf holds a fixed number of disk drives.
Backup appliances based on a scale-up architecture usually require lower amounts of storage capacity for an initial deployment. If an organization needs more capacity, it adds more disk drives to these storage shelves, up to some predetermined, fixed, hard upper limit. Backup appliances that use this scale-up architecture range from a few terabytes of maximum raw capacity to over multiple petabytes of maximum raw capacity.
Scale-out Benefits and Limitations
A scale-out architecture, sometimes referred to as a hyper-converged infrastructure (HCI), enables a company to purchase more nodes as it needs them. Each time it acquires another node, it provides more memory, compute, network interfaces, and storage capacity to the existing solutions. This approach addresses enterprise needs to complete increased backup workloads in the same window of time since they have more hardware resources available to them.
This approach also addresses concerns about product upgrades. By placing all nodes in a single configuration, as existing nodes age or run of capacity, new nodes with higher levels of performance and more capacity can be introduced into the scale-out architecture.
Additionally, an organization may account for and depreciate each node individually. While the solution’s software can logically group physically nodes together, there is no requirement to treat all the physical nodes as a single entity. By treating each node as its own physical entity, an organization can depreciate physical over a three to five-year period (or whatever period its accounting rules allow for.) This approach mitigates the need to depreciate newly added appliances in a shorter time frame as is sometimes required when adding capacity to scale-up appliances.
The flexibility of scale-out solutions can potentially create some management overhead. Using a scale-out architecture, an enterprise should verify that as the number of nodes in the scale-out configuration increases, the solution has a means to automatically load balance the workloads and store backup data across all its available nodes. If not, an enterprise may find it spends an increasing amount of time balancing the backup jobs across its available nodes
An enterprise should also verify that all the nodes work together as one collective entity. For instance, an enterprise should verify that the scale-out solution offers “global deduplication”. This feature deduplicates data across all the nodes in the system, regardless of on which node the data resides. If it does not offer this feature, the solution will still deduplicate the data but only on each individual node.
Finally, an enterprise should keep its eye on the possibility of “node sprawl” when using these solutions. These solutions make it easy to grow but an enterprise needs to plan for the optimal way to add each node as individual nodes can vary widely in their respective capacity and performance characteristics.
Scale-up Benefits and Limitations
Backup appliances that use a scale-up architecture have their own sets of benefits and limitations. Three features that currently working in their favor include:
- Mature
- Well-understood
- Widely adopted and used
One other broader backup industry trend currently also works in favor of scale-up architectures. More enterprises use snapshots as their primary backup technique. Using these snapshots as the source for the backup frees enterprises to do backups at almost any time of the day. This helps to mitigate the night and weekend performance bottleneck that can occur when forced to do all backups at the same using one of these appliances as the backup target.
A company may encounter the following challenges when working with scale-up appliances:
First, it must size and configure the appliance correctly. This requires an enterprise to have a good understanding of its current and anticipated backup workloads, its total amount of data to backup, and its data retention requirements. Should it overestimate its requirements, it may end up with an appliance oversized for its environment. Should it underestimate its requirements, backup jobs may not complete on time or it may run out of capacity, requiring it to buy another appliance sooner than it anticipated.
Second, all storage capacity sits behind a single controller. This architecture necessitates that the controller be sufficiently sized to meet all current and future backup workloads. Even though the appliance may support the addition of more disk drives, all backup jobs will still need to run through the same controller. Depending on the amount of data and how quickly backup jobs need to complete, this could bottleneck performance and slow backup and recovery jobs.
Make the Right Backup Appliance Choice
In order to make the right choice between these two architectures, the choice may come down to how well you understand your own environment. If a company expects to experience periods of rapid or unexpected data growth, using a scale-out appliance will often be a better approach. In these scenarios, look to appliances from Cohesity, Commvault, ExaGrid, NEC and StorageCraft.
If a company expects more predictable or minimal data growth in its environment, scale-up backup solutions such as the Asigra TrueNAS and Unitrends appliances will likely better match its requirements.