Editor's Note: Following is the final in a series of tips about storage virtualization taken from a white paper by Robert Nieboer of StorageTek. This document is frequently requested by searchStorage discussion forum users.
Virtualization: What are you getting for your money? (Part 4)
By Robert Nieboer
The third alternative for the "where" of storage virtualization is in the storage device itself. This is an interesting implementation. If virtualization is done here, and the vendor is a storage vendor, then there are some challenges to avoid limiting the storage devices to just those supplied by the vendor. The storage vendor implementing storage virtualization might form a strategic alliance with a server vendor, a software vendor, or a network vendor to avoid creating a proprietary lock-in.
Today there are two types of implementations of device-level virtualization where logical devices and physical devices exist within the span-of-control of the virtualization engine. These are virtual disk and virtual tape.
The continuing poor utilization of storage resources in enterprise-class disk environments today is matched by inefficient overhead caused by historical and new practices. Typically, only 80% of capacity is actually allocated to files and data bases. That leaves 20% of capacity never allocated and reserved for growth factors. An additional 20% to 30% is wasted by being allocated for files that never grow to fill that capacity. That means that between 40% and 50% of available disk capacity may never be utilized.
Point-in-time copies, used by many hardware and software vendors to minimize recovery times in the event of data loss, can double the amount of capacity needed to satisfy application requirements. Application development challenges IT organizations to provide whole files and databases to test against, again consuming capacity. Time-to-market for new applications is also impacted by how often test files and databases can be reset after test failures.
This poor utilization of capacity and increasing amount of overhead are exactly the kind of infrastructure cost issues that can be addressed by virtualization implemented at the device level and leveraging a span-of-control that includes both logical devices and physical resources.
In tape today, virtualization is being introduced primarily to improve cartridge capacity utilization now that cartridges can cost $100. The unanticipated bigger benefits of tape virtualization have been application performance, and the ability to achieve 100% tape automation by leveraging existing libraries and drives to automate those cartridges that were still within a manual environment. This latter factor alone justifies the use of virtual tape in UNIX and NT.
Questions to ask vendors of virtualization solutions implemented within the storage device:
- Will this solution support other vendor storage devices?
- Are there I/O bandwidth limitations?
- Are there processor bandwidth limitations?
- Which server platforms and operating systems are supported?
- What storage capacity is supported?
- Can multiple subsystems communicate with each other or share resources?
- Is capacity utilization maximized? Is capacity overhead eliminated?
- How is availability ensured?
- Are there any storage management functions carried out within the engine? If so, what functions?
* View this white paper in its entirety.
* Check out the searchStorage Featured Topic on Virtualization.
* Browse links to other virtualization resources.
About the author: Rob Nieboer is a corporate evangelist for StorageTek, and is currently responsible for global industry analyst relations for the company. Rob's background includes some 34 years as an IT practitioner, with the last 17 years focused on storage. His career with StorageTek has included responsibilities for systems engineering, systems engineering management, worldwide tape and library marketing, regional marketing, and strategy.