IBM Storage Virtualization


  In almost every company these days there are three important issues that need to be taken care of. One is containing cost and the others are to control the increasing complexity and to ensure high availability. This is specifically true in environments where multiple different host operating systems and heterogeneous storage is involved.

One important role in this area can be played by IBM’s SAN Volume Controller (SVC).

This short article describes the advantages of the SVC in today’s modern storage environments.

SAN Volume Controller Figure
SAN Volume Controller can help to keep applications running continuously

Today you have to take the storage offline to migrate data or change the storage infrastructure. SVC's data migration capabilities allow you to change your storage infrastructure without stopping your applications, which avoids the cost and impact of this downtime. The SVC can also automatically allocate more capacity to an application that needs it so the business continues to run without interruption. Multi vendor storage arrays can be integrated with no host compatibility impact. Out-of-date and unreliable storage can be removed/replaced without downtime.

SAN Volume Controller can help to contain cost

The Enterprise Strategy Group found that early adopters of storage virtualization on average saved 24% on hardware costs, 16% on software and 19% on SAN administration annually. The hardware cost savings come from a better utilization of the storage pool under SVC control. ‘Thin Provisioning’ or ‘Storage Overallocation’ and ‘Space-Efficient Flashcopy’ enables also to save real storage space. The software savings come from replacing the operating systems multipath drivers (e.g. Powerpath) with the free of charge Subsystem Device Drivers used for the SVC. Additionally, if multiple heterogeneous advanced functions (Flashcopy and/or Remote Mirroring) are used, they can be consolidated into the SVC advanced copy functions. Another cost factor is the ability to have a common management platform for all underlying storage.

SAN Volume Controller provides disaster recovery and high availability

The SVC supports Metro- and Global Mirroring of Vdisks. Snapshots are supported as well. One unique function is that the RAID-1 support of Vdisks enables copies on different Mdisks. With this functionality a mirror can be made available on another storage subsystem, therefore protecting the applications from a total outage of one storage subsystem.

SAN Volume Controller can help to improve the overall performance

There are basically two methods to do Storage Virtualization:
Out of Band Virtualization, which means the virtualization device is not in the datastream and the I/Os can be done directly between the servers and the storage devices (after the specific host software received the metadata information about the relevant storage location). There is no latency involved for the actual read/write activities. However, the definition and the error recovery is more complex than with
In Band Virtualization. Here the device is within the datastream. The latency per I/O is between 40 and 60 microseconds, which is usually not more than a 1% delay compared to a direct I/O. However, being in the datastream has the advantage to be able to use the 8 GB cache of the SVC, which in many environments improved the overall performance (sometimes drastically). The SVC achieved at a recent industry independent SPC-1 benchmark a new record I/O rate of 272,505 IOPS. The SVC is also leading by far the number of Storage Virtualization installations.


Let’s take a look at two quotes:
“The value of storage virtualization is so compelling that it will reinvent storage networking. Having discrete, individual storage systems to manage and support will one day be viewed as archaic and impractical.” Tony Asaro, Enterprise Systems Group
“It [the SVC] has dramatically simplified our technical architecture and taken out cost and complexity. The performance of SATA disk arrays is noticeably improved over direct attachment.” Cable and Wireless

Wolfgang Singer
Member of the IBM Technical Experts Council

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