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Modular or Monolithic? With VSP, It’s Not Either/Or but AND

by Hu Yoshida on Feb 3, 2011

Recently, a customer showed me an EMC slide that described Hitachi VSP as monolithic storage architecture versus the modular architecture of the VMAX. The implication was that monolithic was bad while modular was good. Another misconception is that modular systems can scale while monolithic systems do not scale.

It is understandable why EMC uses that definition since their DMX fits their monolithic description while the VMAX fits their modular scale out description. In EMC’s case you must have separate storage systems to fit these different requirements.  Hitachi provides both in one storage system, Virtual Storage Platform.

Monolithic and Modular — The Difference

Monolithic storage architectures are composed of multiple processors that share a global cache and can scale up to meet the increasing I/O demands of mainframes or multicore processors that are driven by multiple virtual machines. Modular storage systems are two controller storage systems with separate caches that were originally designed to support open systems workstations. Recently some vendors have loosely coupled modular storage systems together over some type of external switch to provide the ability to scale out.

From a storage view, this loose coupling seems to be an easy way to add capacity, cache, and storage ports. However, from an application perspective this doesn’t help since an application works with a LUN, which is locked behind the cache of one of the Storage systems.  It doesn’t matter how many other storage systems are loosely coupled together because the application cannot access them. In order to satisfy the increasing I/O demands of an application, you need a monolithic architecture that can tightly couple additional resources into a single storage resource pool. Loose coupling also requires the addition of an entire storage node. You cannot incrementally add cache boards, storage ports, or processor boards without adding a complete storage node.

VSP can scale incrementally by adding pairs of central processor blades, I/O port processor blades, back end processor blades, cache modules, and disk modules as required. These storage resources are tightly coupled through an internal switch matrix to provide monolithic scale up. Multiple applications also can be supported with modular increments from a common pool of storage resources. VSP can also scale deep through virtualization of external storage systems, which can be integrated into this common pool of resources.


EMC must maintain the DMX for monolithic requirements and a VMAX for modular requirements. Their scale out also requires the addition of storage nodes, two controller storage systems. With VSP, we have a storage system that can satisfy both requirements with the ability to scale in increments of blades or modules.

VSP can start with two VSD blades, two FED blades and two cache modules with no internal disks and scale out from there by adding pairs of blades and modules. The VMAX starts with a controller frame and a disk frame.

So the next time you see EMC trying to paint VSP as monolithic, I hope you’ll point them to this post and remind them that modular vs. monolithic is not an either/or proposition.  What do you think?

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Comments (2 )

Vinay Babu on 07 Feb 2011 at 9:05 am

Very true… Facts are directly proportional to Truth where as SLIDES are indirectly proportional to SALES :-)

Both Monolithic and Modular architectures have their own pros and cons. But its the sales / field force which portrays that one is good and the other is bad. An intelligent customer will buy the product based on his CAP-EX, ROI, Service support and finally but not the least Performance!

Hu Yoshida on 08 Feb 2011 at 12:01 pm

Hello Vinay, thanks for your comments. I would also add one more point that may be covered under your point about ROI. That is the ability to enhance your existing storage assets with new functionality through storage virtualization. This is what my friend David Merrill refers to as ROA, return on assets: http://blogs.hds.com/david/2010/02/roi-and-roa.html

Today we announced the availability of VMware VAAI support on our VSP platform: http://blogs.hds.com/hu/2011/02/unleashing-the-power-of-hitachi-virtual-storage-platform-to-vaai.html. We provide the capability to make your existing storage assets enabled for VAAI through the virtualization of the VSP. Check it out. The ROA will be in the additional VMware scalability and performance that you will achieve on your existing storage, VMware, and server assets.

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