Storage Concepts: Software Defined Storage (SDS)

What is SDS?

Software Defined Storage, or SDS, is now integral to most virtualisation technologies. Indeed, the term is often used interchangeably with “Storage Virtualisation” – rightly or wrongly is material for another article. SDS could be said to define the suite of tools available to virtualise storage than the virtualisation itself, but I will confine this article to speaking interchangeably about SDS and storage virtualisation. As with all “Software Defined…” concepts, the key premise is abstraction, in this case of physical storage, and its presentation as a pool of usable data storage that can be allocated to devices, often through automation at the virtualisation layer. A much over-used expression is the Single Pane of Glass (SPOG) but it is applicable here in that SDS software provides an overall view of the storage without the need to monitor and manage individual storage devices. The software, quite literally, defines how the storage is allocated and used.

How is SDS used?

Imagine an environment with a mature storage estate that comprises a number of disparate storagedevices, let’s say EMC VNX, IBM V7000 and HDS HUS300, managed across several management platforms (EMC Ionix, IBM Flex System Management, Hitachi Device Manager, etc.). There is a big push for virtualisation through VMware but the storage side needs to remain in place until the virtualisation project is completed. Freeing up space from the virtualisation project, through consolidation, archive etc; means that these existing storage systems are more than adequate to service requirements of the virtualised platform. SDS software can aggregate the storage from all three storage devices and allow control of provisioning through the virtualisation software. The storage is aggregated into pools and provisioning can be manually or automatically done, depending on the organisation’s needs, entirely through the virtualisation software which in this case would be VMware vSphere. I guess I should say that other platform virtualisation technologies are available. Whether I believe it or not.

Automation

There is a high level of automation available to those who wish to virtualise their storage. It is possible, though maybe not always advisable, to allocate multiple tiers of storage into a large pool and let the underlying storage take care of the tiering. Consider a datastore has been created from a virtualised storage pool containing tier 1, 2 and 3 storage – let’s say a couple of EMC VNXs and an HP P4335 (odd mix, but you know how these things often happen). The storage can be pooled and allocated to a subset of virtual machines which all have differing storage performance requirements (IO profiles if you will) and the underlying storage will take care of the location of the storage through automated tiering of areas of high activity and performance requirement (hot-spots). Those virtual machines, after a period of learning, will have their performance requirements automatically met, assuming there is enough higher tier storage available.

Virtual Storage Appliances

Virtual Storage Appliances (VSA) are used to perform the storage virtualisation function. These will take an underlying storage system and allow it to be used with the abstraction layer’s software capabilities. One example of which would be where cross-site clustering is required but existing storage is unable to perform the synchronicity required to keep everything up to date. Implementing a VSA to sit above the storage and manage the replication and synchronisation allows a lower cost, cross-site storage solution to be implemented. Whether a low cost implementation of business critical clustered applications is appropriate is a discussion for those who will be picking up the bill.

Is SDS New?

As with many technical innovations, they are variations on an old theme. Mainframe computing used the concept of storage virtualisation way back in the ‘70s, believe it or not. IBM’s MVS (which stands for Multiple Virtual Storage) made use of shared memory across many virtual systems and workloads. Storage meant “memory storage” in this case but the principle was much the same. Storage systems as we would recognise them were still some way off.

What SDS Solutions Are Out There?

Here are a few of the better known SDS vendors:

• Nexenta
• Symantec (Storage Foundation/InfoScale)
• DataCore
• VMware
• EMC (ViPR, vVNX)
• HP (StoreVirtual VSA)

All provide the ability to centralise storage management and provide overall control of the storage landscape to virtualisation platforms. Some of these may be contentious and open to argument around whether they truly offer software defined storage, but they all put in a pretty good claim.

This article details these vendor’s offerings, and more, rather well.

Who Uses SDS?

Pretty simple to answer – anyone who requires a high level of automation, simplification and abstraction from their storage environment. That would include:

• Cloud service providers
• Anyone wishing to virtualise their estate
• Anyone with heterogeneous, legacy storage environments
• Anyone with a wide range of performance requirements

Anyone who wants to simplify storage management, in a nutshell.