A NAS aggregator acts, in effect, as a gateway for a series of NAS boxes or NAS gateways. NAS aggregators allow you to consolidate files stored on NAS devices into a single domain. That, in turn, allows you to add more NAS storage and to easily manage files stored on NAS.
The actual installation of a NAS aggregator is no more complicated than adding a NAS gateway. But, you have to make a lot of decisions about the structure of your new NAS storage environment and how you want things to function before you perform the installation.
Consider the following points carefully when selecting and installing a NAS aggregator:
NAS aggregators are best employed where there are NAS systems from multiple vendors, and you want a high degree of consolidation.
In those cases, aggregators are extremely useful and can save you money and management headaches. However, the more you depart from that picture, the more the problems inherent in aggregators are likely to affect you.
NAS aggregators aren't cheap, especially the hardware ones, and they all have to be managed. Hardware or software, they add another layer of complexity to your storage systems and the in-band ones can limit your NAS bandwidth.
Although most aggregators can be used in tandem to provide failover, a standalone aggregator, especially one of the hardware ones, introduces a single point of failure into your NAS system.
Before deciding on an aggregator, you should consider other options. If you're consolidation needs aren't too extreme you may be better off simply moving up to a larger NAS appliance or gateway.
Like virtual file systems, NAS aggregators introduce major changes into the storage architecture, at least at the virtual level. By combining the view of files stored on various NAS file systems, aggregators require storage administrators to rethink how this storage is organized.
This isn't a matter of physically changing the location of the files in storage, but it does reorganize the view of the file system that administrators and users work with.
Making the best use of this capability requires careful planning. In fact, you should probably map out the new structure before you select an aggregator, so you can choose one which will best support the file views that you want to give.
A few products, like Acopia's, support remote mirroring between aggregators. Most don't. If remote mirroring is part of your data protection scheme you need to take that into account.
Most aggregators, like those from Acopia and NuView (now part of Brocade), allow you to automatically migrate files between aggregators, often with fairly sophisticated policy management. This can be important if you need to balance the loads among aggregators, but it requires that you plan for such migration. Again, this is probably something you want to look at before you select your hardware to make sure your aggregator can support your proposed configuration.
Aggregators can be in-band, like Acopia and NeoPath or out-of-band, like NuView, or even a hybrid like EMC's Rainfinity RainStorage.
With an in-band aggregator, reads and writes flow through the appliance on the way to and from the storage. This can create a bandwidth problem and it adds overhead to storage operations.
Out-of-band aggregators don't require that reads and writes go through the aggregator, relying on a file system service such as Windows Active Directory to provide the global name space needed to consolidate files. This means they don't limit the bandwidth of storage operations. However, out-of-band products can't see as deeply into the data and typically can't automatically migrate files from one NAS system to another. (NOTE: 'system' means either a standalone NAS appliance or a NAS gateway.)
EMC's RainStorage is usually an out-of-band appliance, but it uses an in-band technique to migrate files. However, the RainStorage isn't completely automatic like the purely in-band aggregators.
About the author: Rick Cook specializes in writing about issues related to storage and storage management.
This was first published in September 2007