When saving information for an organization, the major tradeoff comes between the cost of storage and the amount and type of information stored. Storage efficiency is obtaining the most possible storage for the least possible cost. An organization that is storage efficient can hold more data on their drives without impacting performance or cost on the total network system. In general, increasing storage efficiency will decrease expenditures within the organization, allowing the company to more effectively maximize the potential of their hardware.
Storage efficiency is determined by using a fairly simple equation. To calculate the storage efficiency of an organization, a person must simply add together the effective capacity of the organization's hardware plus the available free capacity of the hardware. The result is divided by the stated raw capacity of the hardware to reach the storage efficiency percentage, provided in decimal format. Most organizations fall within the 40 to 70 percent range.
To understand how storage efficiency can be compromised through higher-level organizational storage techniques, a redundant array of inexpensive disks (RAID) storage system can be considered. Many companies use mirroring, which is a RAID storage technique in which information is written to two or more hard drives concurrently, providing a real-time backup for all data in the company. This effectively halves the storage capacity of the hard drives being used, as two 160 gigabyte (GB) hard drives — which would normally afford 320 GB of raw storage — only provide half of that on a RAID system, as both drives are effectively working as a single "mirrored" volume. In terms of the storage efficiency equation, a RAID volume using mirrored drives would only provide 50 percent efficiency; the actual 160 GB mirrored storage potential divided by the theoretical 320 GB storage maximum for the independent drives.
Techniques exist to increase storage efficiency within a system, reducing the cost of storing data on a drive. One such technique is snapshot technology, which, instead of saving multiple copies of an altered file, only saves the actual changed values between a file. So while a "normal" backup system would save two complete versions of an altered database file — the old and the new — a snapshot would only save a single instance, followed by a smaller file denoting the changes made to the file.