The primary benefit of scalable NAS solutions is being able
to increase capacity while maintaining a global namespace and providing access
to one coherent file storage pool. Capacity is increased by adding more nodes
to the storage pool where typically new nodes are similar to existing ones in
terms of memory and storage capacity. It is important to note that while adding
nodes can increase bandwidth capacity, the bulk of data is still retrieved from
disk and therefore adding nodes to a clustered file server does not decrease
latency.
But does the latency remain the same? Herein lies the problem: as more nodes are added, the overhead of coordinating file operations between the nodes increases. Therefore, latency increases as more nodes are added to a clustered NAS solution. Regardless of the implementation, clustered NAS solutions must coordinate file coherency between the nodes since data modifications by one of the nodes must somehow be synchronized with the other nodes to make certain that no data corruption takes place. Even when reading data, overhead exists to either propagate or coordinate the read requests to the correct node. And as node count increases, the chance that a file request would initially be sent to the right node decreases, making request propagations more frequent.
So how do you enjoy the capacity scale of clustered NAS
solutions without being impacted by increased latency?
This is where a scalable, centralized caching appliance can
comes to the rescue. As opposed to other solutions, a caching appliance serves
data direct from memory instead of disk, thereby reducing latency to sub-milliseconds
response times. Furthermore a central appliance does not need to coordinate
file operations between other appliances/nodes and can guarantee high
performance levels regardless of the capacity and scale of the underlying file
system. With a centralized caching appliance enhancing a clustered NAS
solution, capacity can be scaled and managed with a global namespace while
performance also scales and high bandwidth and low latency levels can be
maintained. A centralized caching appliance also provides the benefit of being
able to scale performance by growing the cache without the need to
over-provision capacity in the storage system as well.
So do clustered NAS solutions really scale? Definitely, they
scale in capacity and data management. But if you want to also enjoy the
benefit of performance management and scale, nothing can replace the need for
centralized caching.
