The aim of this blog post is to try to iron out some
misunderstandings in two common terms in storage. Two terms that are actually
really rather connected; storage
virtualisation and software-defined
First let's deal with storage virtualisation. Here at
ComputerWeekly.com we're pretty certain that there's a good deal of confusion
about this term. In our yearly poll of readers we keep hearing that "storage
virtualisation" is a key priority on IT department to-do lists for the coming
year that figure was 36%.
That figure seems unusually high. It's an un-scientific
measure, for sure, but as a storage journalist I get a fairly good idea of the
type of projects that are hot by what comes across my desk, by speaking to
customers, and to vendors, and I just don't hear much about storage
So, when those questioned in our poll ticked "storage
virtualisation", what many probably thought we were asking was "is storage for
virtualisation a priority?" Why? Because server and desktop virtualisation is a
big priority for a lot of organisations right now and implementing storage and
backup to support it is a key part of that process.
Meanwhile, storage virtualisation products allow
organisations to build storage infrastructure from multiple vendors' hardware.
Storage suppliers, of course, would prefer that they provided all of your disk
systems. Consequently, while the key storage vendors have storage
virtualisation products, it's not something they push particularly hard in
marketing or sales terms.
Storage virtualisation products include EMC's VPLEX, IBM's SAN
Volume Controller (SVC), NetApp's V-Series and Hitachi's VSP.
There are also the smaller storage virtualisation vendors
and products, such as DataCore's SANsymphony, Seanodes' SIS, FalconStor's NSS
and Caringo's CAStor.
These are all reasonably well-established products that
allow users to create single pools of storage by abstracting the physical
devices upon which they are layered to create a virtual storage array.
More recently, we've seen that capability emerge in the form
of products at a higher, environment level.
Here, I have in mind, for example, VMware's
plans for Virtual SAN, which will allow pooling, from the hypervisor,
of server-attached disk drives, with advanced VMware feature integration, such
as high availability and vMotion.
It will scale to petabyte levels of capacity and will put some pressure on
existing storage vendors playing in the SME up to small enterprise levels when
it come to fruition.
And there is EMC's
ViPR environment, announced at EMC World 2013, which merges storage
virtualisation with big data analytics. Key to this discussion is ViPR's
ability to pool storage from direct-attached hard drives, commodity hardware
and other vendors' arrays into one single reservoir of storage that's
manageable from a single screen.
These initiatives contain a large dose of what has for a
long time been called storage virtualisation but are billed as software-defined
So, to what extent are either of these terms accurate
reflections of the technology they represent?
Well, of course both terms could be said to be so vague to
be almost meaningless. After all, all storage is based on the retention of data
on a physical drive, but that would be nothing without software that
abstracted/virtualised for example, blocks and files to physical media, RAID
groups and LUNs.
In other words storage never exists without being defined by software or being
virtualised in some sense.
So, how do we make sure we're using these terms clearly?
Well, on the one hand it seems reasonable that storage virtualisation should
refer to the abstracting of multiple vendor systems into a singly-manageable
pool of storage. If there's anything such as historical usage in storage and IT
then those systems ranging from IBM's SVC to the likes of DataCore seem to fit
that billing and have done for some time.
Meanwhile, while we can recognise that VMware's planned
Virtual SANs and EMC's ViPR are heavily based on storage virtualisation capability
as defined here, they also go beyond this, to incorporate much higher level
features than simple storage functionality, such as vMotion and big
data analytics respectively.
Despite the efforts of some vendors, notably DataCore, which
has gone from dubbing its products a "storage hypervisor" to software-defined
storage according to the whims of the IT marketing universe, it seems
reasonable to define storage virtualisation as quite narrowly as centring on the
ability to pool heterogeneous media into a single storage pool.
Meanwhile, software-defined storage can be reserved for higher
level function and environment-type products that also include storage
It's always a battle to define terms in an area so fast
moving as IT, and with multiple vested interests and active marketing departments,
but it's certainly valid to try and define terms clearly so the customer is
able to see what they're getting.