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What is RAID Storage: RAID Technology Explained

Data storage and Data sharing has become easier over the past several decades, but it is still possible to lose critical data. If critical data is stored on a single hard drive and that hard drive fails, data is lost.  This is s problem, and RAID technology is one solution to this problem.

Short for Redundant Array of Independent Disks, RAID technology links multiple hard drives together so that an operating system sees them as one single, large hard drive. By doing this, users can save data in multiple locations across drives, increasing the speed at which the system can read files, and protecting data in the event of hard drive failure.

It is important to understand what RAID is and what RAID is not.  RAID is an array of disks configured to offer protection against drive failure and/or increase performance.  Depending on the RAID level implemented, a RAID array can suffer the failure of one to two disks and the array will remain functional.  There is usually a degradation of performance of the RAID array for a period of time until the failed disk is replaced and the array is rebuilt.

RAID is not a substitute for back up.  RAID is not a method for disaster recovery.  If a catastrophic event such as a fire or tornado destroys the building, the best RAID implementation will lie in ruins with the rest of the building.

Software RAID and Hardware RAID

RAID can be implemented using software, which runs as another task, a task to which the CPUs in a server must devote resources.  RAID can also be implemented using specialized RAID hardware, usually a card installed in a server.  Software RAID is the slower of the two choices.  Software RAID must compete with and wait on the other software tasks that are going on in a server, and software RAID adds more processing burden to the system, slowing down other tasks.  If performance is a consideration (and most often it is), software RAID is not the best choice.  The use of hardware RAID will not only result in better performance, it can allow the introduction of caching that can further increase performance.  Hardware RAID can also offer additional functionality over software such as the ability to alert users to drive and I/O errors remotely.  This can mean the difference between having the opportunity to prevent a failure and having to react to a failure.

RAID Storage Redundancy Techniques Protect Data

There are several different techniques that RAID stores data, including the use of mirroring, striping, and parity, and there are levels of RAID that incorporate combinations of these techniques. Each has pros and cons, and ultimately the individual IT professional has to decide which method is best for a given application.

Mirroring involves copying data onto a second hard drive, so that if one drive fails, the data is still available on the other. One advantage of mirroring is that two complete sets of data are contained in the array, maximizing redundancy. One disadvantage of mirroring is that it is not efficient in terms of disk space.

Striping data is another method RAID can utilize to store data. As a file is written, parts or stripes of data are written across several disks. Writing these stripes can be done simultaneously which will increase performance. Striping alone does not provide any redundancy. If a disk is divided into 4 parts, and each part is stored on a different disk, when one disk fails, the data is lost.

Parity can be utilized with striping to add a level of redundancy. As the stripes of data are written across multiple disks, parity data is calculated and written across the disks as well. If a drive fails, this parity data can be used to keep the array functioning. Obviously writing additional data takes time and impacts performance. When the failed disk is replaced, the array must rebuild itself, and this process takes time. The larger the array, the more time it takes. Still, the ability to sustain the loss of one to two disks in the array without losing all data on the array makes striping and parity an attractive choice for many applications.

There are a number of RAID levels which combine and nest mirroring, striping, and parity in order to maximize data availability and fault tolerance.

Who Should Use RAID Technology?

The casual PC user might not necessarily need RAID, but this technology is an incredible boon to data centers and enterprises whose success depends on them having fast, reliable access to large amounts of data. In some settings, such as a hospital that uses electronic records and medical imaging, immediate access to data can actually be a life and death matter.

RAID is Only One Part of Protecting Data

IT professionals should evaluate all methods of maintaining data integrity and maintaining uptime, and Implement those that fit their needs. RAID is usually part of the mix of methods that will deliver the desired result.  Other methods include onsite and offsite backups, snapshots and other techniques to insure data can be recovered in case of events ranging from disk failure to catastrophic natural disaster.

Nfina’s servers, NAS products, and SAN products all have RAID storage and caching options to help users ensure that their critical data is protected and readily available.

If you believe that your business or organization could benefit from enhanced RAID technology, request a quote today.