Some systems are born with high availability, others have it thrust upon them. This seems to be the case when discussing the High Availability (HA) features of traditional NAS systems vs those of object storage systems. HA refers to the ability of a system to be available for an extended period of time, surviving many of the things that would take lesser systems down. Even the cheapest systems have some type of HA features built into them. They are able to survive the loss of a component or two. For example, if a disk drive, power supply, or controller fails, there are redundancies built in to be able to survive the failure.
The true test of an HA’s system mettle, however, is what happens when an entire node or site fails. Will the system continue to serve its purpose and preserve the data? The answer for NAS systems is maybe and, if so, the HA features were thrust upon them. That is, HA is an add-on to the original design of a system.
NFS and SMB, the protocols designers use to build NAS systems, were both initially designed in 1984. They both think of a NAS server in the same way, it is a computer with a hostname and a single IP address. While we have figured out ways around that, the client still believes it is communicating with a single server. This creates multiple problems, including not being able to scale performance farther than a single node, and not being able to use HA features — without doing some fancy footwork.
There are certainly NAS vendors that can scale beyond a single node and there are those that have built HA features into their NAS products as well. It includes multiple nodes that monitor each other through some kind of heartbeat monitor. In an active-passive configuration, the passive node takes over for the active node if it were to fail. In an active-active configuration, both nodes are sharing a portion of the production load. If one node goes down, the remaining node(s) take(s) over the extra load created by the loss of the one node. But the NAS client has no idea any of this is happening, because it is still talking to the same IP address it was talking to before an issue arose. This is accomplished through some type of mask that hides the true IP address of the actual node delivering the service.
This is why some say that NAS systems have HA thrust upon them. It is a bolt-on feature added decades after the initial design, and is still in many ways a workaround to the fact that NFS and SMB clients think they are talking to a single server.
Object storage, on the other hand, is from this century, and has HA features built into it. Customers can specify what level of redundancy their system needs to have, and one part of the system does not have to lie to any other part of the system for things to actually work. An object storage client understands that it is talking to a multi-node system and can adjust accordingly if one of the nodes in an object storage system were to become unavailable. And since all data is replicated to multiple locations, any node in any location can satisfy any read request.
NAS systems play an important role in today’s data centers, but adding HA to the mix requires a lot of additional hardware and software that needs masking from the NAS client. Object storage systems, on the other hand, are built with HA in mind. If HA is the goal, perhaps object storage systems would be a more appropriate tool.
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