Storage Virtualization Definition
Simply, it is the ability to have single point of management for all storage devices. At its core, the storage virtualization layer pools physical storage from multiple, heterogeneous network devices and presents a set of volumes for hosts to use (regardless of the storage brand). In addition to creating storage pools composed of physical disks from different arrays, storage virtualization provides a wide range of services, delivered in a consistent way, that include:

  1. Basic volume management (including LUN masking, concatenation, volume grouping and striping across multi vendor storage arrays)
  2. Support for tiered storage
  3. Non-disruptive data migration
  4. Data protection and disaster recovery functionality, such as snapshots and Asynchronous, Semi-synchronous, or Synchronous mirroring

Storage virtualization addresses and solves the five challenges, discussed previously in the first part of this article hindering the management of a large enterprise-class storage environment.

Where Virtualization Lives
Storage virtualization services, like volume management, snapshots and replication, can reside at the host, network, or storage device level. Traditionally, storage intelligence has lived at either the host-level with a software volume manager, like Veritas Volume Manager, or in the RAID controller or a storage device.
However, with the advent of network-based storage virtualization, this intelligence is being pushed into the network layer.
IBM System Storage SAN Volume Controller (SVC) is the crown jewel in IBM’s storage strategy and portfolio, launched in July 2003.
IBM boasts a fourth generation product with over 14,000 SVC systems implemented and five years of market acceptance. SVC is widely viewed as the most successful storage virtualization in the market today. These statistics speak to the maturity of the product and the value of a high touch consulting approach.
SVC is 4Gbps End-to-End system that virtualizes 4Gbps storage arrays as well as auto negotiating down to 2Gbps speed, if necessary. SVC support up to 1024 attached hosts (servers) running any operating system where system capacity can grow up to 8 Peta Bytes.
The SVC is based on a clustered, redundant, highly scalable architecture. It is only deployed in clustered pairs of nodes (each with 8GB of cache) running SVC software. A pair of SVC nodes is known as I/O group. In order to ensure redundancy, single node configuration isn’t supported. Adding another I/O group (that is, two SVC nodes) increases cluster performance and bandwidth. Therefore customers can start small and scale as their storage needs and I/O throughput profile changes over time.
SVC comes with the full breadth of features most users expect from a storage virtualization product, including snapshots in the form of FlashCopy, thin provisioning by way of Space Efficient Virtual Disks (SEVs) and synchronous or asynchronous replication via Metro Mirror or Global Mirror. These features are in addition to the fundamental storage capabilities of storage pooling, provisioning, volume mirroring, and volume copying/migration.

SVC Architecture
SVC is known as an In-Band virtualization appliance that has proven superiority in performance over other techniques implemented in other systems. It has shown that In-Band approach with a large amount of mirrored cache can indeed scale to handle the most stringent enterprise IOPS and availability requirements. For example, SVC boasts the highest IOPS rate (272,500 IOPS SPC-1 Benchmark) as measured by the Storage Performance Council SPC-1 Benchmark. The SPC-1 benchmark simulates read-write random I/O workloads, like Online Transaction Processing (OLTP) database and email and in an accurate approximation o a typical enterprise I/O pattern. SVC has also laid claim to the top spot (7.08 GB/s SPC-2 Benchmark) SPC-2 is a benchmark that simulates large, sequential I/O processing. Moreover, IBM’s SVC team has a big focus on availability, and their efforts were touched by customers. To date, field data across all deployed SVCs demonstrates availability comparable to or better than enterprise-class disk systems. IBM, through its focus on performance, scalability, and availability approaches has shown that an In-Band approach to virtualization can, in fact, scale and meet the availability demands of the large and small enterprises.
SVC’s highly scalable In-Band architecture, and robust feature set and capabilities provide the following crucial benefits to end users that differentiate SVC from the other virtualization players :

  1. Central Storage Virtualization across heterogeneous storage pools with the ability to stripe data across different systems to have higher performance
  2. Central control point for multivendor storage arrays
  3. Seamless Tiered Storage solution taking off the headache from administrators managing data across different tears
  4. Always On-Line Storage Infrastructure by providing Non-Disruptive data Migration
  5. Thin provisioning across multiple storage systems to make full use of storage resources.
  6. Data protection and Disaster Recovery solution using different vendors’ storage arrays

Of the most storage vendors, IBM has been the most aggressive in terms of insisting on the benefits of storage virtualization and helping to drive awareness and adoption of the technology delivering SVC to market while it was protected by IBM support engineers. IBM SVC is a fourth generation product that has prospected where other storage virtualization products have struggled. It is a truly enterprise-tested product as evidenced by the more than 14,000 deployed systems with customers.
In short, storage virtualization is coming of age and SVC is well positioned o capitalize on the trend. IBM is already the dominant supplier of storage virtualization today and has the most mature, robust, widely supported offering in the market place. But, this success has not gone unnoticed by other vendors, who have accelerated their product introductions and development now that IBM has blazed the trail to success.

By: Mohamed El Mofty
Storage Networking Solutions Expert
IBM Systems and Technology Group