RAID Levels Explained

Topics: RAID, Network-attached storage, Computer storage Pages: 5 (1479 words) Published: October 2, 2014
If you've ever looked into purchasing a NAS device or server, particularly for a small business, you've no doubt come across the term "RAID." RAID stands for Redundant Array of Inexpensive (or sometimes "Independent") Disks. In general, a RAID-enabled system uses two or more hard disks to improve the performance or provide some level of fault tolerance for a machine—typically a NAS or server. Fault tolerance simply means providing a safety net for failed hardware by ensuring that the machine with the failed component, usually a hard drive, can still operate. Fault tolerance lessens interruptions in productivity, and it also decreases the chance of data loss.

The way in which you configure that fault tolerance depends on the RAID level you set up. RAID levels depend on how many disks you have in a storage device, how critical drive failover and recovery is to your data needs, and how important it is to maximize performance. A business will generally find it more urgent to keep data intact in case of hardware failure than, for example, a home user will. Different RAID levels represent different configurations aimed at providing different balances between performance optimization and data protection.

RAID Overview
RAID is traditionally implemented in businesses and organizations where disk fault tolerance and optimized performance are must-haves, not luxuries. Servers and NASes in business datacenters typically have a RAID controller—a piece of hardware that controls the array of disks. These systems feature multiple SSD or SATA drives, depending on the RAID configuration. Because of the increased storage demands of consumers, home NAS devices also support RAID. Home, prosumer, and small business NASes are increasingly shipping with two or more disk drive bays so that users can leverage the power of RAID just like an enterprise can.

Software RAID means you can setup RAID without need for a dedicated hardware RAID controller. The RAID capability is inherent in the operating system. Windows 8's Storage Spaces feature and Windows 7 (Pro and Ultimate editions) have built-in support for RAID. You can set up a single disk with two partitions: one to boot from and the other for data storage and have the data parition mirrored.

This type of RAID is available in other operating systems as well, including OS X Server, Linux, and Windows Servers. Since this type of RAID already comes as a feature in the OS, the price can't be beat. Software RAID can also comprise virtual RAID solutions offered by vendors such as Dot Hill to deliver powerful host-based virtual RAID adapters. That's a solution more tailored to enterprise networks, however.

Which RAID Is Right for Me?
As mentioned, there are several RAID levels, and the one you choose depends on whether you are using RAID for performance or fault tolerance (or both). It also matters whether you have hardware or software RAID, because software supports fewer levels than hardware-based RAID. In the case of hardware RAID, the type of controller you have matters, too. Different controllers support different levels of RAID and also dictate the kinds of disks you can use in an array: SAS, SATA or SSD.

Here's the rundown on popular RAID levels:

•RAID 0 is used to boost a server's performance. It's also known as "disk striping." With RAID 0, data is written across multiple disks. This means the work that the computer is doing is handled by multiple disks rather than just one, increasing performance because multiple drives are reading and writing data, improving disk I/O. A minimum of two disks is required. Both software and hardware RAID support RAID 0, as do most controllers. The downside is that there is no fault tolerance. If one disk fails, then that affects the entire array and the chances for data loss or corruption increases.

•RAID 1 is a fault-tolerance configuration known as "disk mirroring." With RAID 1, data is copied seamlessly and simultaneously, from one...
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