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A Primer on Today’s Storage Array Types

Anyone who managed IT infrastructures in the late 1990’s or early 2000’s probably still remembers how external storage arrays were largely a novelty reserved for high end enterprises with big data centers and deep pockets. Fast forward to today and a plethora of storage arrays exist in a variety of shapes and sizes at increasingly low price points. As such it can be difficult to distinguish between them. To help organizations sort them out, my blog entry today provides a primer on the types of storage arrays currently available on the market.

The large number of different storage arrays on the market today would almost seem to suggest that there are too many on the market and that a culling of the herd is inevitable. While there may be some truth to that statement, storage providers have been forced to evolve, transform and develop new storage arrays to meet the distinctive needs of today’s organizations. This has resulted in the emergence of multiple storage arrays that have the following classifications.

  • Enterprise midrange arrays. These are the original arrays that spawned many if not all of the array types that follow. The primary attributes of these arrays are high availability, high levels of reliability and stability, moderate to high amounts of storage capacity and mature and proven code. Features that typify these arrays include dual, redundant controllers, optimized for block level traffic (FC & iSCSI), and hard disk drives (HDDs).  These are generally used as general purpose arrays to host a wide variety of applications with varying capacity and performance requirements. (The most recent DCIG Buyer’s Guide on midrange arrays may be accessed via this link.)
  • Flash memory storage arrays. These are the new speed demons of storage arrays. Populated entirely with flash memory, many of these arrays  can achieve performance of 500,000 to 1 million IOPS with latency at under a millisecond.

The two potential “gotchas” here are their high costs and relative immaturity of their code. To offset these drawbacks, many providers include compression and deduplication on their arrays to increase their effective capacity. Some also use open source versions of ZFS as a means to mature their code and overcome this potential client objection. Making these distinctively different from the other array types in this list of array types is their ability to manage flash’s idiosyncrasies (garbage collection, wear leveling, etc.) as well as architecting their controllers to facilitate the faster throughputs that flash provides so they do not become a bottleneck. (The most recent DCIG Buyer’s Guide on flash memory storage arrays may be accessed via this link.)    

  • Hybrid storage arrays.  These arrays combine the best of what both flash memory and midrange arrays have to offer. Hybrid storage arrays offer both flash memory and HDDs though what distinguishes them from a midrange array is their ability to place data on the most appropriate tier of storage at the best time. To accomplish this feat they use sophisticated caching algorithms. A number also use compression and deduplication to improve storage efficiencies and lower the effective price per GB of the array. (The most recent DCIG Buyer’s Guide on hybrid storage arrays may be accessed via this link.)
  • Private cloud storage arrays. Private cloud storage arrays (sometimes referred to as scale-out storage arrays) are defined by their ability to dynamically add (or remove) more capacity, performance or both to an existing array configuration by simply adding (or removing) nodes to the array.

The appeals of these arrays are three-fold. 1.) They give organizations the flexibility to start small with only as much capacity and performance as they need and then scale out as needed. 2.) They simplify management since administrators only need to manage one logical array instead of multiple smaller physical arrays. 3.) Organizations can mitigate and often eliminate the need to migrate data to new arrays as the array automatically and seamlessly redistributes the data across the physical nodes in the logical array.

While these arrays possess many of the same attributes as public storage clouds in terms of their data mobility and scalability, they differentiate themselves by being intended for use behind corporate firewalls. (The most recent DCIG Buyer’s Guide on private cloud storage arrays may be accessed via this link.)

  • Public cloud storage gateway arrays. The defining characteristic of these storage arrays is their ability to connect to public storage clouds on their back end. Data is then stored on their local disk cache before it is moved out to the cloud on some schedule based upon either default or user-defined policies.

The big attraction of these arrays to organizations is that it eliminates their need to continually scale and manage their internal storage arrays. By simply connecting these arrays to a public storage cloud, they essentially get the capacity they want (potentially unlimited but for a price) and they eliminate the painful and often time-consuming need to migrate data every few years. (A DCIG Buyer’s Guide on this topic is scheduled to be released sometime next year.)

  • Unified storage arrays. Sometimes called converged storage arrays, the defining characteristic of these storage arrays is their ability to deliver both block (FC, iSCSI, FCoE) and file (NFS, CIFS) protocols from a single array. In almost every other respect they are similar to midrange arrays in terms of the capabilities they offer.

The main difference between products in this space is that some use a single OS to deliver both block and file services while others use two operating systems running on separate controllers (this alternate architecture gave rise to the term “converged.”) The “unified” name has stuck in large part because both  block and file services are managed through a single (i.e. “unified“) interface though the “converged” and “unified” terms are now used almost interchangeably.. (The most recent DCIG Buyer’s Guide on midrange unified storage arrays may be accessed via this link.)

Organizations should take note that even though multiple storage array types exist, many storage arrays exist that satisfy multiple classifications. While no one array model yet ships that fits neatly into all of them, DCIG expects that by the end of 2014 there will be a number of storage array models that will. This becomes important to those organizations that want the flexibility to configure a storage array in a way that best meets their specific business and/or technical requirements while eliminating the need for them to buy another storage array to do so.


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