High end enterprise storage systems are designed to scale to large capacities, with a large number of host connections while maintaining high performance and availability. That takes an architecture where a host can access any storage port and have direct access to a number of storage controllers which can service I/O requests and process their data services requirements. This takes a great deal of sophisticated technology and only a few vendors can provide such a high end storage system. Hitachi’s, high end, Hybrid Virtual Storage Platform (VSP) G1500 and All Flash VSP F1500 arrays provide this capability which is made possible through a switch architecture which dynamically connects front end ports with controllers and a global cache with backend device controllers.
For the midrange user where cost is a key factor and massive scalability is not required, the architecture has to be changed to trade off scalability for reduced cost. However, that trade off often means that some advanced enterprise functions like distance replication and zero data loss recovery would be compromised. With recent advances in Intel multicore technology and PCIe extensions, it is now possible to scale down these systems to reduce costs while still providing these advanced enterprise functions. The recent models of the Hitachi Vantara VSP Hybrid G and All Flash F series storage arrays, now provide, cost efficient, scaled down versions of the G1500 and F1500 Enterprise storage arrays, without any loss in enterprise functionality. This was done by consolidating the VSP controller, cache memory, and interconnects onto a cost optimized, two controller architecture which utilizes Intel’s latest multicore processors with high speed PCIe interconnects. These two controllers are configured as Active/Active controllers, which means that any I/O can access any device through either controller.
Midrange storage arrays are configured with dual controllers for availability. However, there is a great deal of difference in how the two controllers are configured. Most are configured as Active/Passive or Asymmetric Logic Unit Access Asymmetric (ALUA). Very few are Active/Active. The configuration of the storage controllers is a key differentiator when it comes to the performance and functionality of the storage system. Here are the differences between the different types of controller configurations.
The VSP’s Active/Active configuration is made possible through the concatenation of the cache that is attached to each controller. Both controllers work with the same cache image of the storage LUN. This configuration is also known as Active/Active Symmetric since both controllers can process the I/O request versus the prior ALUA asymmetric configuration above. This requires additional routing information that is provided by the Storage Virtualization Operating System that is available in all models of the VSP series. This Active/Active capability provides many benefits. We don’t need to worry about LUN ownership as in the case of asymmetric controllers. This provides the ability to use VMotion for live migration of running virtual machines between servers that don’t have identical primary failover controller assignments, with zero downtime, continuous service availability, and complete transaction integrity. This also provides the ability to load balance across a SAN without the worry of creating a performance issue on the storage. Since the VSP can virtualize external storage, this also makes it possible to process a cache image of a LUN from an externally attached storage system. This ability to virtualize external storage enables the extension of the useful life of legacy storage systems and the non-disruptive migration of data to and from an external systems as I posted in a previous blog.
The latest versions of our midrange offerings, the Hybrid VSP G350/G370 and All Flash VSP F350/F370 come in a cost effective 2U of rack space with the enterprise features of our high end and over 1 million IOPS for the VSP F370. All priced and packaged for the midrange.
On the higher end, which many refer to as the entry enterprise, we offer the Hybrid VSP G700/G900 and All Flash VSP F700/F900 that can scale to 2.4 million IOPS and comes in 4U of rack space. The differences in the model numbers is based on the number of Intel processors and cores. Both Hybrid and All Flash entry enterprise models have the same dual controller Active/Active design as the midrange models but with many more Intel cores, memory, front end ports, back end ports, and higher internal bandwidths. Here are the specifications for the Entry Enterprise Models.
The Hybrid VSP G1500 and All Flash VSP F1500 are included to show the full scale out capability of their switch architecture. The VSP G/F1500 is a multi-controller architecture in which the processors, memory modules, front end ports and back end ports are all connected through an internal non-blocking, cross bar, switch, which enables a LUN to be accessed directly through any port without the overhead of passing control between controllers.
There are other architectures which support more than two controllers, but those types of architectures involve a great deal of overhead and complexity. Without an internal switch architecture, no matter how many controllers you hook together, I/O requests for a LUN still have to be processed through the controller that owns the LUN. So If your I/O request comes in from another controller port, the I/O has to be passed to the controller that owns the LUN, creating more overhead and complexity with each additional controller that is added. Having two controllers adds redundancy but adding more controllers to a two controller architecture, can create less availability since the cumulative failure rate increase with each added controller. Having two controllers fail independently is rare, and a two controller failure is usually due to a base failure which would affect all the controllers no matter how many you have.
In the case of the VSP G/F1500 the switch architecture would allow the controllers, cache, and LUNs to be assigned dynamically and fail independently.
The VSP family of storage arrays, provides a choice of cost optimized configurations from midrange to high end scalable enterprise systems, all running the same software and providing the same functionality to help our customers preserve their investments in policies and procedures and leverage their ecosystem-related investments. Although there is a difference in architectures we are able to simulate the architectural differences in software so that all the models have the same functionality even when it is scaled down to the midrange price and packaging. Our dual controller architectures are fully Active/Active which differentiates us from many other midrange and entry enterprise systems.