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  Site Maintenance Hosting Services RAID - A Laymans Guide

RAID - A Laymans Guide

mordcomm Hosting Services Oct 11, 2004

What is RAID?

RAID - A Laymans Guide

The acronym RAID means R edundant A rray of I ndependent (or I nexpensive) D isks. When originally developed at the University of California at Berkeley in 1987, the word was “ I nexpensive,” referring to the fact that it was basically an array (or group) of relatively inexpensive disk drives grouped together in such a way that to the computer it appeared to be one very large (and thus very expensive) hard drive. Comparatively speaking, the cost of hard drives is now much less, so when you mention “RAID,” your colleague is most likely thinking “Redundant Array of Independent Disks.” Five levels of RAID were originally defined, each providing different trade-offs in features and performance.

Why Is RAID Important?

There are two main purposes to RAID – a method of storing the same data in different areas (which is where the word “Redundant” comes in), and a way to speed up and stabilize your computer's performance. Through trial and error, the Berkeley group developed different types of RAID that balanced the need for increased performance with the desire for more reliability in data storage.

One might think that with today's high-speed and large capacity drives, RAID would no longer be relevant. However, transfer rates and capacity of current individual drives cannot keep pace with the continuingly increasing need for data storage capacity and high speed data access. RAID is still the best answer to the question of how to provide quick access to a lot of stored data at a reasonable cost, with the added plus of data protection.

RAID is not necessarily easy to install and maintain on your own computer system, but if you have ever had a hard drive crash, you know how costly in time and effort it is to restore the data on that hard drive. Current web hosting packages usually include RAID protection of some kind, which is reflected as the percentage of “uptime” a web host claims to offer.

What Types of RAID Are Available?

There are a number of variations of RAID, each with its own individual advantages and disadvantages, but the ones listed below are the basic building blocks for other variations.

  1. RAID Level 0 is based on a method called “striping,” which breaks all the data on your computer into smaller chunks of data that are placed across all available disk drives. Its biggest advantage is that the small packages of data scattered across a number of drives can be very quickly pulled together into a coherent whole.

The biggest disadvantage to RAID 0 is that even if just one of the drives in the system fails, you in effect lose all of your data, since at least part of it would have been stored on the drive that has failed.

  1. RAID Level 1 introduces the benefit of “mirroring,” or copying all of your data onto at least one another drive, perhaps even onto many other drives. This ensures that your data will be duplicated in whole on at least one other hard disk, so if your data is lost in a disk failure, there is at least one extant copy immediately available. RAID Level 1 documents usually have enhanced read times as well. If fault tolerance is the key benefit you are looking for, RAID 1 is the most basic level that offers this feature.

The biggest disadvantage to RAID 1 is the cost of having additional disk drives containing the mirror of your data.

  1. Combination of RAID Levels 0 and 1

A combination of both RAID 1+ 0 employs mirroring and striping methods – making sure you will not lose all your data if a hard disk fails and also giving you the spanning capacity of multiple hard disks – all at speeds faster than possible from a single disk. This combination offers the best of both worlds.

4. And there is also RAID 5, which is often viewed as the ideal mix of good performance, good fault tolerance, high capacity and storage efficiency. Reason being that RAID 5 stripes both data and parity information across three or more drives.

In today's web hosting packages, some form of RAID is usually included as a standard part of the package, so do not be surprised if no specific mention is made of RAID when you sign with a web host. The presence and effectiveness of a web host's RAID system is very closely represented by the host's server uptime. High server uptimes (not to be confused with connection uptimes) typically indicate that a well-managed RAID system is in place.

If you decide that an individualized RAID setup is necessary for your website itself, collaborate extensively with your web host before purchasing the necessary equipment. There are various hybrids of RAID implementations which really are just enhancements of the basic RAID arrays described above.

Is RAID Hardware Better Than RAID Software?

When you are deciding between a hardware versus software RAID solution, the key is to look at the levels of RAID the option provides.

Software RAID usually supports RAID 0 and 1 (speed through striping and fault protection through mirroring). Hardware RAID, however, will include a number of additional data recovery tools – for example, a SCSI-based RAID card will support many RAID levels, each providing a different combination of speed and data protection.

In essence, software control is cheaper and easier to maintain but takes up server processor resources. On the other hand, RAID hardware does the work separately from the server processor, but is more expensive overall.

Do I Need RAID?

Even if your web host provides RAID protection, the best web host can fail – no one can realistically promise 100% uptime. Despite this, as long as the web host has a good uptime rate, most websites do not choose the added expense of their own RAID system.

Generally speaking, the type of websites that may need additional RAID protection are those that deliver critical or time-sensitive news or information on their websites; or those that maintain a database that has large file sizes or high recall rates which are cumbersome or slow to restore in the event of web host hardware failure.

You probably do not need a RAID system of your own if all you do is maintain static textual and graphic content, such as on a company website or a photo album. RAID usually makes most sense for businesses whose websites play a significant role in their profitability. Some examples include websites that need to store large amounts of data and want it to be quickly and reliably available to them, such as industries requiring high bandwidth, like video production and editing applications, image editing, and prepress applications.

What is the Relationship Between RAID and the Backup of Data?

Whether you decide to install RAID on your computer or not, the most important thing to remember is that RAID is NOT a replacement for a systematic and regular backup process for your computer system. You should be keeping backup copies of all your data locally and making sure that your web host also does regular backups of data.

Take responsibility for ensuring that your data is backed up as frequently as you need (daily backups are of course the ideal) no matter what type of RAID you or your web host maintain. RAID provides improved data storage capabilities and increased fault tolerance, but it is not a substitute for a regular backup procedure in the ultimate goal of keeping all the hard work you have done on your website safe and secure.

   
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