VIRTUALIZATION : Addressing Storage Needs

Given the importance of information, storage solutions have become the order of the day. Partners need to keep finding ways to satisfy the growing storage needs of enterprises. The technology of virtualization offers capacity as well as simple management of storage devices.

Data storage has taken center stage in today´s business environment. In the current business environment, access to the right information at the right time is of utmost importance to remain competitive. Consequently, data storage has evolved significantly over the years, from the erstwhile direct attached storage (DAS) to storage area network (SAN).

STORAGE VIRTUALIZATION

Virtualization technology simplifies management of SAN devices  It reduces TCO and increases utilization of existing storage systems  Simply mapping logical units capacity without taking into account differences in performance can lead to escalation in cost  A storage management framework with open standards enhances its usability

Organizations have benefited greatly from SAN systems. It allows optimum utilization of capacity and also enables disparate storage systems to be viewed as a single storage system. Further, it increases capacity utilization by simplifying connectivity. 

However, these systems need a layer of management for switches. Also, lack of SAN standards and differences in operating platforms as well as storage devices have created substantial problems of manageability and inter-operability. Additionally, storage management costs run six to eight times higher than the acquisition cost of the storage itself. In such a scenario, the industry is very excited about the promise that virtualization technology holds.

STORAGE INTRICACIES

In the traditional devices, storage was directly attached to the server. The excess capacity was often not utilized as it could not be shared between servers. In order to ensure that enough space was always available, each standalone server was provided with excess capacity. This resulted in huge cost overheads, as the storage utilization was to the tune of 30 to 50% only. 

The introduction of SAN significantly increased the utilization capacity through fiber channel network. It helped to connect several storage devices with multiple servers. With this, a pool of storage was created and re-allocated to servers through SAN management tools without physically re-cabling the storage devices. 

However, SAN relies heavily on networking hardware and software such as hubs, switches, and host-bus adapters. These are needed to create a fiber channel for connecting numerous servers. This adds another layer of management for interconnection of the fiber channel hardware and software. Because of this, issues of inter-operability and manageability are created in heterogeneous storage environments.

It is at this point, virtualization promises to ´melt´ down various SAN devices to form a common pool of capacity and simplify management of these devices. 

HOW DOES SAN/VIRTUALIZATION WORK?

When we take a look at different types of storage environments, each of them environments have specific approach models. However, the essential components remain the same.

A storage environment consists of applications, logical components (databases) and virtual volumes and physical (storage disks and tapes). SAN provides an abstraction layer between the application and the logical data. The same happens with virtual resources and the physical storage.

Virtualization enables separation of the logical data and the virtual resources. This type of a model simplifies storage management concerns. It promises to reduce TCO and increase utilization of existing storage systems In addition, this technology promises ´virtual utilization´ with a storage capacity beyond 100%. Users will be charged for an amount for storage but only allocating a portion as it is required.

WHERE TO VIRTUALIZE?

On the implementation of virtualization, different vendors have different opinions about where its capabilities should reside. It could be some say at the server level, fabric level or the and at the storage system level.

Ideally, virtualization must be addressed at the server access and control level. This will allow storage addresses to be remapped and redirected, creating a virtual pool of capacity. This can be managed by discovering, provisioning and maintaining the data path between the application and the storage.

Nowadays, IT managers use capacity as a tool for managing storage, instead of making capacity the end for management. For example, the transaction performance of a revenue-producing application should not be used for capacity demands of a messaging application. At the same time, the productivity of employees should not be stifled by limitations on storage capacity in a messaging application. 

Therefore, the productive use of storage virtualization should be focused on managing the growing explosion of data, rather than on limiting it.

ISSUES IN IMPLEMENTATION

There are many point solutions in the market for implementing virtualization across a heterogeneous storage environment. However, they are not complete. It is because simply mapping logical units (LUN) capacity without taking into account the differences in performance of various devices can lead to escalation in cost and decrease in revenue.

Consider the Figure 1 which depicts two server clusters running on two different OS platforms. Servers A and A’ form a cluster on one type of OS, with alternate paths to virtual volume A. Volume A is virtualized across storage array E and storage array C, sharing portions of disks W, X, Y, and Z. Servers B and B’ are in a different cluster with another OS that uses alternate paths to virtual volume B. Volume B is virtualized across storage arrays E and C and shares portions of disks W, X, Y, and Z.

The first problem in such an architecture is that there is the need for many more dedicated ports than would have been if the clusters were directly attached. This is necessary because the storage ports need to understand the command language of the particular platform they are connected to. Additionally, the servers must have a path to each physical part of a virtual volume.

Secondly, the problem with a heterogeneous storage system is that some of the platforms might be faster than the others. This would make the virtualization performance quite unpredictable. And, apart from this, different systems might have different scaling characteristics as the load increases. All these aspects make recovery very unpredictable and erratic, normally resetting the pending input/output to a physical device.

However, when we consider a virtualization architecture wherein the servers are direct attached to the storage, the effect is dramatically different. This kind of architecture introduces two elements–the virtual storage ports and host storage domains. The former supports the connection of heterogeneous platforms to each storage port. 

A specific mode is no longer required as a fabric switch in SAN can direct multiple heterogeneous platform servers to a single port on the storage system. Using the host storage domains, a mode set can be specified at the storage domain level so that it can converse with the corresponding server platform. This kind of a feature can provide separate, secure, storage pools for separate host groups.

HOW TO HANDLE THIS VIRTUE?

Even though there are such features that make access to virtualization easy and obliterate many of its flip-sides, additional intelligence should be added to the management or control side of this technology. This is the real challenge of virtualization. 

One of the ways to tackle this challenge is to provide a storage management framework, which will be based on open standards such as common information model and simple object access protocol. It provides enterprise storage seekers with the choice of going in for best-of-the-breed solutions as well as collaborating with multiple storage vendors. 

This approach to virtualization will simplify management of storage. However, as IT continues to grow, so will the storage needs of enterprises. And hence, continuous research on developing scalable, reliable and high-performance storage systems will have to be on.

P P Subramanian is the Country Manager,
Hitachi Data Systems, India