Yes, SAN Does Suffer from Fragmentation

SAN brings many benefits to an enterprise. Stored data does not reside directly on a company’s servers, therefore business applications get the server power, and end users obtain the network capacity that would otherwise be utilized for storage. Administration is more flexible, because there is no need to shift storage cables and devices in order to move storage from one server to another. Servers can even be booted from the SAN itself, greatly shortening the time required to commission a new server.

There are numerous technologies employed to make SAN efficient, including RAID,  I/O caching, snapshots and volume cloning, which have lead some to believe that SANs do not suffer the effects of file fragmentation. Fragmentation is the splitting of files into pieces (fragments) originally developed for the purpose of better utilizing disk space in direct attached storage devices.

The problem is that data is read and written by the operating system, and this is done on a logical, not a physical level. The OS’s file system, by its very nature, fragments files. While the data from the viewpoint of the NAS may appear efficiently arranged, from the viewpoint of the file system it is severely fragmented—and will be treated as such.

Fragmentation affects computer operations in numerous ways. Chief among them is performance; due to the fact that files must be written and read in thousands or even hundreds of thousands of fragments, performance is severely slowed down. In a fragmented environment, unexpected system hangs and even disk crashes are common. A heavy toll is taken on hardware, and disks can lose 50 percent or more of their expected lifespans due to all the extra work.

In past times, the solution to the fragmentation issue was a defragmenter. Because of many innovations in today’s computing environments—such as those used with SAN—a higher-level solution is needed. An optimization solution, which addresses a broader scope of issues than fragmentation only, is required.

Such a solution approaches numerous aspects of file read and write I/Os in addition to fragmentation. The majority of fragmentation itself is prevented before it even occurs, but also included is the intelligent ordering of files for faster access, along with other advanced technologies designed to automatically maximize system performance and reliability.

The best proof of fragmentation’s effects on SAN is through the testing of an optimization solution within an enterprise. Doing so, it will be clearly seen that fragmentation does indeed affect SAN operations—and they can only benefit from its elimination.

Balancing the Powerful Simplicity of SAN with Fragmentation Prevention

As with everything in computing, one of the primary goals developers have for storage area networks (SANs) is simplicity. SAN continues to advance with the advent of self-optimization, virtualization, storage provisioning and other benefits which make the technology more automatic. As SAN becomes more accessible and affordable, more companies are taking advantage of its many benefits.

The whole idea of a SAN, of course, is moving storage away from production servers, thereby freeing up resources for active company traffic. High-speed fiber channel networks make it possible for the switch to SAN to be invisible to the user, simply because speeds are similar to direct attachment of disks. Again, the goal is simplicity.

If file fragmentation is not addressed with an equally simple and powerful approach, this goal becomes less obtainable. All of this advanced technology must still read files from hard drives. Due to the splitting of files into thousands or tens of thousands of fragments, unnecessary complexities are introduced into the scheme. And access speed—another prime goal of a SAN—is nullified.

The various technologies being employed to assist SANs in being faster and more automatic each have their own unique susceptibility to fragmentation. For example, thin provisioning allows advance allocation of disk space. But at the same time, the file system may simply write data wherever space is to be found. If data is written to a “high” logical cluster number (say, cluster 200), all clusters from zero to 200 will be allocated even if not used. When data is added to an old file, new files are added or deleted, or an old file is expanded, the difference between file system disk allocation and storage system thin provisioning can contribute to fragmentation, over-allocation, and less efficient use of storage space.

Another example is virtual machines. At the very least, file I/Os are passed through a host and a guest system; file fragmentation wreaks havoc by adding multiple I/Os where there are already plenty extra.

Technology such as SAN requires an equally powerful—and simple—fragmentation solution. Following the trend of full automaticity, the most beneficial solution today is one which functions fully automatically, in the background, requiring no intervention from IT personnel. It is now even possible to prevent a majority of fragmentation before it occurs, putting its complex issues thoroughly in the past.

A SAN can now bring a robust resource saving storage solution to any site. As a companion, the fragmentation solution employed must be comparably robust—and simple.