4 Keys To Storage Management

Chapter 12: Storage Management

This excerpt is abridged.

Storage Management

More than most other systems management processes, storage management involves a certain degree of trust. Users entrust us with the safekeeping of their data. They trust that they will be able to access their data reliably in acceptable periods of time. They trust that, when they retrieve it, it will be in the same state and condition as it was when they last stored it. Infrastructure managers trust that the devices they purchase from storage-equipment suppliers will perform reliably and responsively; suppliers, in turn, trust that their clients will operate and maintain their equipment properly.

We will interweave this idea of trust into our discussion on the process of managing data storage, beginning with four major areas:

Recoverability plays a fundamental role in disaster recovery. Many an infrastructure has felt the impact of not being able to recover yesterday's data. How thoroughly we plan and manage storage in anticipation of tomorrow's disaster may well determine our success in recovery.

We begin with a formal definition of the storage management process and a discussion of desirable traits in a process owner. We then examine each of the four storage management areas in greater detail and reinforce our discussion with examples where appropriate. We conclude this chapter with assessment worksheets for evaluating an infrastructure's storage management process.

Definition of Storage Management

Storage management is a process used to optimize the use of storage devices and to protect the integrity of data for any media on which it resides.

Optimizing the use of storage devices translates into making sure the maximum amount of usable data is written to and read from these units at an acceptable rate of response. Optimizing these resources also means ensuring that there is an adequate amount of storage space available while guarding against having expensive excess amounts. This notion of optimal use ties in to two of the main areas of storage management: capacity and performance.

Protecting the integrity of data means that the data will always be accessible to those authorized to it and that it will not be changed unless the authorized owner specifically intends for it to be changed. Data integrity also implies that, should the data inadvertently become inaccessible or destroyed, reliable backup copies will enable its complete recovery. These explanations of data integrity tie into the other two main areas of storage management: reliability and recoverability. Each of these four areas warrants a section of its own, but first we need to discuss the issue of process ownership.

Storage Management Capacity

Storage management capacity consists of providing sufficient data storage to authorized users at a reasonable cost. Storage capacity is often thought of as large quantities of disk farms accessible to servers or mainframes. In fact, data storage capacity includes main memory and magnetic disk storage for mainframe processors, midrange computers, workstations, servers, and desktop computers in all their various flavors. Data storage capacity also includes alternative storage devices such as optical disks, magnetic drums, open reel magnetic tape, magnetic tape cartridges and cassettes, digital audio tape, and digital linear tape. When it comes to maximizing the efficient use of data storage, most efforts are centered around large-capacity storage devices such as high-volume disk arrays. This is because the large capacities of these devices, when left unchecked, can result in poorly used or wasted space.

There are a number of methods to increase the utilization of large-capacity storage devices. One is to institute a robust capacity planning process across all of IT that will identify far in advance major disk space requirements. This enables planners to propose and budget the most cost-effective storage resources to meet forecast demand. Another more tactical initiative is to monitor disk space usage to proactively spot unplanned data growth, data fragmentation, increased use of extents, and data that has not been accessed for long periods of time. There are a number of tools on the market that can streamline much of this monitoring. The important element here is the process, rather than the tool, that needs to be enforced to heighten awareness about responsible disk space management.

The advent of the personal computer in the 1970s brought with it the refinement of portable disk storage beginning with the diskette or so-called floppy disk. Early versions were 8 inches wide, stored 80 kilobytes of data, and recorded only on one side. Refinements eventually reduced its size to 3.5 inches and increased its capacity to 1.44 megabytes. By 2001, both Sony Corporation and Phillips Electronics had refined and offered to consumers the universal serial bus (USB) flash drive. These devices were non-volatile (they retained data in absence of power), solid state, and used flash memory. More importantly, they consumed only 5 percent of the power of a small disk drive, were tiny in size, and were very portable. Users have come to know these devices by various names, including:

Storage Management Performance

There are a variety of considerations that come into play when configuring infrastructure storage for optimal performance. The following list shows some of the most common of these. We will start with performance considerations at the processor side and work our way out to the storage devices.

The first performance consideration is the size and type of main memory. Processors of all kinds -- from desktops up to mainframes -- have their performance impacted by the amount of main storage installed in them. The amount can vary from just a few megabytes for desktops to up to tens of gigabytes for mainframes. Computer chip configurations, particularly for servers, also vary from 128MB to 256MB to forthcoming 1GB memory chips. The density can influence the total amount of memory that can be installed in a server due to the limitation of physical memory slots.

In smaller shops, systems administrators responsible for server software may also configure and manage main storage. In larger shops, disk storage analysts likely interact with systems administrators to configure the entire storage environment, including main memory, for optimal performance. These two groups of analysts also normally confer about buffers, swap space, and channels. The number and size of buffers are calculated to maximize data-transfer rates between host processors and external disk units without wasting valuable storage and cycles within the processor. Similarly, swap space is sized to minimize processing time by providing the proper ratio of real memory space to disk space. A good rule of thumb for this ratio used to be to size the swap space to be equal to that of main memory, but today this will vary depending on applications and platforms.

Channels connecting host processors to disk and tape storage devices vary as to their transfer speed, their technology, and the maximum number able to be attached to different platforms. The number and speed of the channels influence performance, response, throughput, and costs. All of these factors should be considered by storage management specialists when designing an infrastructure's channel configurations.

Tape and disk controllers have variable numbers of input channels attaching them to their host processors, as well as variable numbers of devices attaching to their output ports. Analysis needs to be done to determine the correct number of input channels and output devices per controller to maximize performance while still staying within reasonable costs. There are several software analysis tools available to assist in this; often the hardware suppliers can offer the greatest assistance.

A software methodology called a logical volume group assembles together two or more physical disk volumes into one logical grouping for performance reasons. This is most commonly done on huge disk-array units housing large databases or data warehouses. The mapping of physical units into logical groupings is an important task that almost always warrants the assistance of performance specialists from the hardware supplier or other sources.

To improve performance of disk transactions, huge disk arrays also have varying sizes of cache memory. Large database applications benefit most from utilizing a very fast -- and very expensive -- high-speed cache. Because of the expense of the cache, disk-storage specialists endeavor to tune the databases and the applications to make maximum use of the cache. Their goal is to have the most frequently accessed parts of the database residing in the cache. Sophisticated pre-fetch algorithms determine which data is likely to be requested next and then initiate the preloading of it into the cache. The effectiveness of these algorithms greatly influences the speed and performance of the cache. Since the cache is read first for all disk transactions, finding the desired piece of data in the cache -- for example, a hit -- greatly improves response times by eliminating the relatively slow data transfer from physical disks. Hit ratios (hits versus misses) between 85 percent and 95 percent are not uncommon for well-tuned databases and applications; this high hit ratio helps justify the cost of the cache.

Two more recent developments in configuring storage systems for optimal performance are storage area networks (SANs) and network attached storage (NAS). SAN is a configuration enhancement that places a high-speed fiber-optic switch between servers and disk arrays. The two primary advantages are speed and flexibility. NAS is similar in concept to SAN except that the switch in NAS is replaced by a network. This enables data to be shared between storage devices and processors across a network. There is a more detailed discussion on the performance aspects of these two storage configurations described in Chapter 8, "Performance and Tuning."

To read Chapter 12 in full, click here.

Chapter 12: Storage Management is is an excerpt from
IT Systems Management,
by Rich Schiesser, published by Prentice Hall Professional

Infrastructure expert and world acclaimed author Rich Schiesser combines the expertise of a senior IT executive, professional educator, industry spokesman and sought-after consultant to benefit numerous clients in a variety of industries world-wide.