Chapter 6. Storage Virtualization: Where Are Your Files and Applications?
What Is Storage Virtualization?
Our journey into the layers of virtualization continues and we have reached the bottom of the model. The remaining two layers of virtualization technology touch all of the others. This time, we’re going to examine storage virtualization (see Figure 6-1). Storage virtualization refers to the tools used to present an artificial view of the storage environment.
Storage virtualization often is supported by storage servers. Clients and servers need not know where the files they’re processing really reside. They also need not know what type of storage device holds their applications and data. The storage devices could be based on rotating media, such as traditional disk drives, or solid state technology, such as SSDs or dynamic random access memory (DRAM).
Once again, this technology was originally developed for mainframe systems in the late 1960s, was recreated on minicomputers (now called midrange machines) in the 1980s, and started appearing on industry-standard systems (X86-based) in the early 1980s. The industry is still in the middle of a transition from server- or client-attached storage to virtual storage that is located in the network.
This type of virtualization is often used in conjunction with several other types.
What Does Storage Virtualization Do?
As shown in Figure 6-2, storage virtualization creates an artificial view of the network that hides the physical network from clients and servers. It provides the following functions:
- Allowing distributed file systems
Remote storage devices are made to look like they were directly attached to the system. The local system does not know where they are located or what type of storage device they are.
- Creating artificial storage volumes
Multiple storage devices can be harnessed together to create the image of a single, much larger storage device.
- Creating arrays of storage volumes
Applications and data can be spread over a number of storage devices and storage servers to improve overall storage performance. This function can also be used to improve storage reliability. The same data can be stored on several storage devices or storage servers. If one storage device or server fails, the data can be reconstructed.
- Allowing greater control of storage space
Storage devices can be segmented into several “file systems,” allowing the storage device to be more fully utilized.
- Allowing incompatible systems to share storage devices
Mainframes, single-vendor operating systems, Windows, Linux, and UNIX all use different mechanisms to store and retrieve applications and data. Storage virtualization makes it possible for all of these to share the same storage devices and the files they contain.
Storage servers are, by the way, computer systems managing a number of storage devices. This allows many general-purpose systems to access the same storage. The storage server’s operating system keeps track of which general-purpose server is allowed to access what data storage on individual storage devices. If these storage servers connect to the general-purpose systems over a special-purpose storage network, the configuration is often called a storage area network (SAN). Storage accessed over a network is called network attached storage (NAS), regardless of whether it is on a SAN or the same local area network (LAN) used by general-purpose systems.
When Should Storage Virtualization Be Used?
Storage virtualization should be used by organizations seeking to achieve the following goals:
- High availability/fail over/disaster recovery
If organizations are deploying application or processing virtualization, it is likely that storage virtualization should also be deployed. When organizations need continuous access to applications and data, if a single storage device, the network used to access that device, or the storage server fails, storage virtualization can press another device, network, or storage server into service.
- Improve storage performance
If application virtualization, workload management, or parallel processing software is deployed to increase overall scalability or performance, storage virtualization should be deployed, too. Today’s distributed applications often assign the same task to many systems. Many systems working together on a single task can overwhelm the storage system. If the workload is spread over many different storage devices, the workload can be handled.
- Making the same storage resource serve everyone
If the organization is deploying many virtual environments, each running on a different type of operating system, storage virtualization should be deployed as well. Organizations typically have a large number of different applications. Each of them may be hosted on a different physical or virtual system. Each of the applications may be hosted on a different operating system, each of which uses storage differently. Storage virtualization is used to make the same storage devices serve many tasks.
Players in the Storage Virtualization World
Although there are many players in the storage virtualization market, a short summary of some of the suppliers follows:
- EMC
EMC began as a company offering third-party memory boards and storage devices for mainframes and minicomputers. Over time, the company created storage servers that could serve the storage needs of many different types of systems.
- Hitachi
Hitachi offers storage devices and storage servers for mainframes, midrange systems, and industry-standard systems.
- HP
HP offers its own storage servers to support its midrange systems and industry-standard systems.
- IBM
IBM has offered its own mainframes, midrange systems, and industry-standard servers. The company offers storage servers and storage devices that can serve the needs of all of its products.
- NetApp
NetApp has long offered storage servers for industry-standard systems and midrange systems from many suppliers.
A Few Examples of Storage Virtualization in Use
There are many different environments in which storage virtualization can be beneficial. The following list contains only a few examples:
- Increasing performance or scale of storage-centric workloads
A transaction-oriented ecommerce application might overwhelm the capacity of a single storage system, so an organization typically spreads the applications and data over a number of storage devices and storage servers. Another approach is to substitute special, high-speed storage technology with devices that use solid state devices (SSD) or dynamic random access memory (DRAM) rather than a spinning disk. These devices may provide latency and throughput similar to the system’s own internal memory.
- Data center optimization
If each server had its own private storage system, a great deal of space would be taken up in the organization’s data center for storage devices. Furthermore, it is likely that these storage devices would be lightly used; that is, a great deal of empty space would be found on each device. To reduce overall costs for storage devices, data center space, power, and heat production, organizations use storage virtualization to share storage devices among all of the servers supporting a given workload.
- High availability/fail over/disaster recovery
Organizations may install redundant storage servers. If any storage device or storage server fails, the storage virtualization function would reroute requests from the failed devices to one of the surviving storage devices or servers.