Hu Yoshida

Achieving the Dream – One Operating System for Midrange to Enterprise Storage

Blog Post created by Hu Yoshida on Apr 28, 2015

As long as I have been in storage, the dream has been to have a common operating system for midrange and enterprise storage.  This would help to reduce development costs and cycles for vendors, while simplifying management, and providing the right price point without sacrificing functionality for end users. However, since midrange storage is targeted at smaller organizations, with smaller IT budgets, midrange storage systems have always required a different architecture with scaled down functionality and availability. This meant that the operating system for the midrange storage systems had to be different, the functionality was limited and different management tools were required. Hitachi has achieved the dream of a common operating system with the introduction of the Virtual Storage Platform (VSP) models G200, G400, G600, and G800, which run the same operating system as the enterprise-class VSP G1000.


The biggest difference in terms of architecture between enterprise and midrange storage are the controllers, which manage the movement of data between the front-end host ports and the back end device ports. Midrange storage controllers consist of a processor with cache memory and a set of front and back-end ports. There are usually two controllers that are clustered together so that storage that is accessed from one controller is mirrored in the other controller for redundancy. The storage must be owned by one controller (active), while the other remains passive to avoid a race condition called thrashing, where controllers contend with each for access and impact performance. While this is a simple way to provide redundancy, it does not provide dynamic load balancing and when one controller fails, the other controller must take on the additional workload and performance suffers. Having only two controllers, also limits the cache, port and processor resources to support other functions like tiering, replication and migration. The Hitachi Unified Storage midrange products solved some of the problem of ownership by transferring the I/O request to the controller with ownership for execution regardless of which controller was initially requested. However, the architecture was still a dual controller with separate caches and ports, and it could not support VSP enterprise functions like virtualization of external storage.


Enterprise storage can have more than two controllers, and the main difference in architectures is a global cache with virtual ports that can be dynamically assigned to different controllers. The cache and ports can be shared by all the controllers for load balancing, and other functions like tiering, replication, migration, and virtualization of external storage. Creating a dynamic infrastructure like this requires additional processing power and sophisticated meta data management to synchronize the access to storage from multiple controllers, the result is higher throughput and access performance, higher scalability, and higher availability, but at a higher cost. The difference in architecture and functionality also means that the operating system in enterprise storage systems is different than the operating system  in midrange systems. In the VSP G1000 enterprise array we utilize custom ASICs to accelerate the internal switching of resources and cache management.  With the VSP G1000 we introduced the Storage Virtualization Operating Systems (SVOS) which acts like a storage hypervisor to create and manage pools of virtual storage internally and externally connected to the VSP G1000, as well as pools of storage that are virtualized across physically separate G1000 systems for global active devices and non-disruptive migration.


With the new models of the VSP (G200, G400, G600, G800) we emulate the ASIC to provide a global cache system using readily available  Intel, multi core, processors with internal levels of cache, QuickPath interconnect and PCIe switching. With this software emulation we are able to use SVOS to provide the same functionality that we have with the G1000 at a lower cost. This includes storage virtualization, active/active configurations using global access devices and non-disruptive migration. While software emulation does introduce some overhead, the trade off is lower cost in hardware and software development and higher availability with only a slight decrease in throughput.




The smallest G200 is housed in a 2U controller module with 64 GB cache and 16 front-end ports, which can scale to 1 PB with 264 drives, and 4080 SAN hosts, bringing it well within the price range of midrange storage, but with enterprise functionality. In addition to storage virtualization, which can extend the VSP functionality to any storage system that attaches to the VSP, all the VSP models can include high performance HNAS 4000 virtual storage file capability for non-disruptive migration and deduplication of NFS or SMB filers. The VSP G200 to G800 are priced and packaged for the traditional mid-range market space with the same common operating system as the enterprise G1000. You can choose the VSP model that meets your requirements based on price and capacity without giving up any functionality. The only difference is mainframe support with FICON reserved for the G1000


Not only has Hitachi achieved the dream of having one operating system, SVOS, for small midrange to very large enterprise storage system, we also have storage virtualization, which can extend the current and future capabilities of this storage operating system to other vendor storage systems, and manage it all through one suite of management tools.


This storage virtualization is a key element to the infrastructure abstraction fundamental to achieving our customers’ need for a software-defined infrastructure, and is built on years of proven success. These new VSP models are included in our Software Defined Infrastructure announcement.