Wednesday, February 19, 2014

A New Definition for Enterprise Storage

A key challenge as Lumenate has grown over the last three years is making sure that the entire organization understands what we sell, where it fits, and our internal technical assessment of each product.  That's a lot of information and requires that we engage in some simplifications.

Historically we have utilized the concept of dartboards, where each type of technology has its own dartboard with the products we represent grouped into one of three categories:

  1. Starter - Products with a proven track record where we have a wealth of knowledge
  2. Second String - Products that we know very well but there may be some "gotchas"
  3. Bench - Products that have a limited use case
One of our dartboards is block storage and part of our evaluation criteria is whether a given technology is considered enterprise or modular.  Whether a given array is enterprise or modular has been ill-defined for some time now - while we used to differentiate on features/functionality even today's entry-level offerings provide what were traditionally enterprise features.

One popular way to differentiate between enterprise and modular is to say that any array that provides mainframe connectivity is enterprise with all other arrays considered modular.  While this has been an accurate distinction, and one that we have historically used, it falls apart when considering Hitachi's HUS-VM.

Although the HUS-VM shares DNA with HDS' traditional enterprise arrays it does not offer a mainframe connectivity option.  By our historical definition then, it is not enterprise.  As we considered the dartboard, though, we felt quite strongly that it was, in fact, enterprise-class storage - but why?  Is there some criteria that it (and other enterprise arrays) meets independent of mainframe connectivity?

My answer to that question is related to the configuration of the array - specifically parity groups.  If there are fixed parity group sizes for availability reasons then an array is enterprise.  Co-opting a popular term - enterprise arrays are engineered systems that provide storage services in a well-defined way.  They are configured in a consistent, repeatable fashion.

In the specific example of the HUS-VM the parity groups may be configured in groups of either 4 or 8 drives (whether FMD, SSD, SAS, or NL-SAS).  These are not arbitrary numbers, but are instead derived from the number of independent back-end links from the controller to the drive trays.  By limiting configuration choices HDS can guarantee availability and optimize performance.  This is a trade-off, exchanging the flexibility of an arbitrary RAID configuration for certainty.  Given the market acceptance of engineered systems, I think it's one most people are willing to make.

I realize that discussing such mundane details as disk parity groups in a software defined world seems contradictory (or put another way "Who cares?").  It's key to realize, though, that as abstraction increases details still matter.


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