Originally posted by: NeilSondhi

The 'Software Defined Storage' (SDS) as says in its wiki (http://en.wikipedia.org/wiki/Software-defined_storage) is:
 "an evolving concept for computer data storage software".

As such any storage vendor and client can see in it different things.
In this blog we give one such an observation of the SDS and how IBM Spectrum Storage™ family offerings, especially the new Spectrum Accelerate fits in.

Some Retro-perspective View:
In the beginning each server/computer had its own [direct attached] storage to manage. Life was easy and the storage was as close as possible to being
"Software Defined/Managed Storage". However, the industry found that dedicated storage was wasteful (as each user gobbled as much disk space as she could while, in reality most of that storage was not used. Also, as disks have their MTBF (Mean Time Between Failure) and do fail pretty often, servicing the disparate devices became unmanageable and the support did not scale up well. To address the above mentioned shortcomings of the "Direct Attached Storage Devices" (DASD) the "Storage Area Network' (SAN) and Network Applied Storage (NAS) were introduced. Using these technologies, the management of the storage was delegated to specialized storage administrators who were responsible for the efficient space allocation and ensuring its availability and resiliency.

Present View:
The new era of NAS and SAN brought about the storage Virtualization where storage arrays are presented to the servers instead of the actual Physical devices. Hence, the operating systems (OS) could not leverage their understanding of the physical disks attributes to for instance, distribute the file system data in a way which gives priority to often accessed data by, placing such data on the external disk tracks or/and cluster related data along the same cylinder to minimize the disks' head moves when the respective data is accessed around the same time.

Now the industry seems to have done a full circle and, by using the "SDS" revolution/evolution concept, attempts are made to bring the "distant" storage devices metaphorically closer to the users. The SAN and NAS architecture are not about to be abandoned as there is merit to their being managed centrally thus, the new technologies goal is to redefine the role of the storage administrators to the minimum necessary for them to maintain the storage devices and at the same time, give the end users as much control as possible over their storage  to use it to their liking.

Heading towards the future
The IBM XIV storage array appliance has accomplished much of those goals when it was introduced years ago.  Using the XIV the users don't need to worry about their data placement neither for performance purposes or for availability reasons. The end user can simply allocate the space they need and the XIV technology transparently handles everything else to perfection without any requirement for manual tuning. Having all data spread across all of the XIV 180 disks ensure both steady state performance without hot spots as well and high reliability where disk rebuild is the fastest possible as all modules and disks share the rebuilding burden of a broken disk and no extra strain is imposed on any of the disks, unlike the legacy type of storage arrays.

One can read more about the XIV revolutionary architecture in other IBM publications such as: http://www.redbooks.ibm.com/abstracts/sg247659.html.  The elegant design and the ease of use of the XIV made it a very attractive storage solution. XIV prides itself of being assembled from standard off the shelf components. This reliance on standard hardware allows XIV to stay the state of the art machine it is for such a long time by, leveraging from all the advancements made in the assortment of components it is made of.

However, as not all storage needs are the same, not all storage solutions can be addressed by one type of storage array, even one as versatile as the XIV is. Though XIV can scale up to hundreds of tera bytes of storage, not every shop needs such a capacity. Also, some clients don't need the latest and the greatest powerful servers or the largest disks the market and XIV has to offer and, can settle for a weaker servers and smaller disks which are already at their disposal and, are strong enough to handle their modest storage needs.

By offering the XIV as a software solution called "Spectrum Accelerate", IBM allows the customers the reuse their pile of standard hardware and quickly setup their own custom made XIV and benefit from the huge investment IBM made in designing and developing the XIV. The XIV appliance and the 'Spectrum Accelerate" can be tied together and provide a seamless total storage solution built on the great XIV technology.