Understanding RAID Levels & Redundancy

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By Linda J
By Linda J
Last Modified July 29, 2019

Data storage hardware isn’t perfect. Unintended losses and errors can make it impossible to access vital information and cripple mission-critical applications. Using a RAID, or redundant array of independent disks, may help data-dependent organizations maintain high availability and improve performance.

Raid Levels: Getting The Most Out Of Redundancy

A Brief Introduction To RAID

RAID configurations create distributed data storage across multiple disks. The earliest implementations were devised at academic institutions in the late 1980s to demonstrate that standard personal computer disks could hold their own against high-end enterprise storage. Today, they minimize load on individual disks, reduce access latency and even provide fast recovery following RAID failures.

How Does RAID Work?

To a computer or network, a group of hard drives in a RAID configuration appears to be a single device, known as a logical unit number, or LUN. LUNs employ various hardware or software techniques, such as:

Parity

Parity is a form of error checking or data redundancy. In RAID, it typically consists of performing logical operations on two drives to generate parity data that’s stored on a third device. Suppose you add the contents of one drive to those of a second and store the results on a third. If drive one or two goes down, you can restore it by subtracting the contents of the remaining good drive from drive three. While this is just an analogy because parity uses logical XOR operations instead of actual binary addition, it illustrates how the concept can be extended to any number of grouped drives.

Mirroring

Simply put, RAID mirroring consists of replicating one set of data on another identical device. As you write information to the main drive, another copy is written to the mirror, which enables professional RAID recovery services to work on it should the main drive fail. Although it naturally increases the amount of time required to write data, mirroring lets you access data faster than one disk can retrieve it by getting parts from each device at top speeds.

Striping

Disk striping takes a chunk of ordered data and splits it up into sections that are then stored on different drives in the array. By writing consecutive sections on different disks, you gain the ability to increase file access speeds by retrieving from each disk simultaneously. This method is not failure proof as it doesn’t include backup data, but it can be used in conjunction with other methods.

RAID Levels | TTR Data Recovery

RAID Levels

So, what are RAID levels and what are the different RAID levels?

RAID levels refer to the different configurations that are used to organize, distribute, and store data in a RAID array. Depending on the RAID level type, the techniques employed could be one or a combination of striping, mirroring, or parity.

The most common types of RAID levels and their advantages/disadvantages:

  • RAID 0
    This type RAID level provides optimum data reading and writing speed improvement but does not provide any form of fault tolerance. This RAID level type is easy to implement requiring no overhead cost.

    RAID 0 is commonly used for non-critical data storage requiring just high speed in reading and writing data such as image and video editing.
  • RAID 1
    Provides fault tolerance by simultaneously creating an exact duplicate of one disk drive to another. RAID 1 provides great read and write speed as well as relatively easy to implement as well.

    RAID 1, however, reduces storage capacity into half as the other half is used to duplicate the data. In case of a failure, hot swapping is not always possible with software RAID 1 as the computer has to be powered down first before the failed drive can be replaced.

    RAID 1 is bet implemented for applications requiring fault tolerance but not needing large storage capacity such as accounting applications.
  • RAID 5
    Commonly used in enterprises. It combines the benefit of fault tolerance and speed by using parity and block-level striping and techniques.

    While the read speed is very fast, write speed is slower due to parity calculations. In case of a drive failure, accessing data is possible while the failed drive is being replaced and data being rebuilt. RAID 5 can only support one drive failure and since rebuilding usually takes time — a day or longer — another disk failure instance is possible.
  • RAID 10
    This RAID level has the same benefits of a RAID 5, as it combines RAID 1 (mirroring) and 0 (striping) — a hybrid, so to speak. RAID 10 secures data by mirroring the data from one drive to a secondary drive while the striping technique allows access to data a fast rate.

    Rebuilding time could take as little as half an hour since you only need to copy the data from the unaffected drive to the new drive. However, as a result of mirroring, storage capacity is reduced to half. This makes implementing RAID 10 more expensive as the number of disks required is double than that of other RAID levels.

Several other different types of RAID levels also exist, which are variants of the previously mentioned basic types of RAID levels, such as RAID 2, RAID 3, RAID 4, and RAID 6.

RAID Level 0 (Stripe Set)

raid-0

RAID 0 is also called striping. It distributes the data across any disks to allow increased data output. A single file is read from various disks to provide access to the speed, as well, as, to the capacity of all the disks. This provides an amplified performance. 

This raid 0 level uses disk striping to spread information evenly over all the disks in an array. It needs two or more disks, and its main purpose is to provide heightened performance as economically as possible. Without redundancy, however, the failure of any single disk will result in the entire volume being lost.

On the other hand, RAID 0 does not allow any type of redundancy and tolerance of fault because it does not reproduce data or store any parity material. In RAID Level 0, both of the disks occur as a single partition, which can result in data loss if one of the disks fail and eventually breaks the array. RAID Level 0 is most commonly employed in caching files that require speed and reliability, such as live streams, among others.

Pros: Improved performance

Cons: Redundancy is not allowed

RAID Level 1 (Mirror)

raid-1

RAID 1 is used for redundancy and performance. Arrays consist of at least two disks with one serving as a mirror. In addition to making it easier to recover information, RAID 1 may reduce seek times by simply pulling specific data from whichever disk is faster or closer to the right position to access the information in question.

RAID 1 is utilized to write and read matching data to pairs of drives. This RAID level is also referred to as data mirroring. Its main function is to allow redundancy that if any of the disks in the array fails, the system will still be able to have data access from other disks. If the damaged disk has been changed, the data can be copied from the undamaged one to the replaced disk. This level is the quickest means to make failover storage.

Pros: Allows data recovery and can tolerate faults. It also increases read performance.

Cons: Capacity with lower usability. Expensive cost due to twice the amount of drives needed to have the required capacity.

RAID 2

raid-2

This RAID level is no longer commonly used. It employs striping at the bit level in conjunction with special error-correcting parity schemes called Hamming Codes to preserve data across synchronized disks.

Advantages of RAID LEVEL 2 are high rates of data transfer; it can also accurately recover corrupted single bit data and if there is an event that a multiple bit corruption occurs, it can be easily detected.

However, the disadvantages of this level include possible corruption of multiple bits; it can detect multiple bit corruption easily but it is not capable of correcting the detected errors; and lastly, it has a very complicated logic of error bit correction. For these reasons, this has become an obsolete data storage method.

RAID 3

raid-3

RAID 3, which is rarely used, stripes data byte-by-byte and includes a dedicated volume for storing parity data. As with RAID 2, disk rotation is synchronized. Its inability to keep up with numerous small requests means it’s most commonly used in media servers and similar setups where data is accessed in long chunks.

RAID Level 3 has several advantages over other RAID levels. For instance, it can provide accelerated read and write speed, especially for the transfer of large files. It is also not as expensive as the other levels. Furthermore, the system of RAID 3 has an efficient hard disks capacity because it only requires one hard disk to store parity bits. On the other hand, RAID Level 3 is not fit to be used for the transfer of small data files. In case that there is a need for data block access, one has to deal with more than one hard drive array.

RAID 4

raid-4

In RAID 4, striping occurs at the block level, and the array includes a volume dedicated to parity info. Its main advantage over RAID 2 and RAID 3 is that it facilitates small transfers since you can perform operations without accessing every single disk.

This RAID Level is somewhat similar to RAID 3 because it also uses a dedicated parity disk. The difference is on how it strips the data – which is at the block level. 

Related Article: Raid Rebuild Guide

Its advantages include providing multiple reads if allowed by the controller to do so; it is cost-effective but this does not entail synchronized spindles.

For the disadvantages, because it only allows access to one block of data at a time, the system is not that quite effective resulting in poor performance. Also, it results in to slow writing of data to disks as parity data must also be entered. 

RAID 5

raid-5

This is one of the most popular and most commonly used RAID Level. Although it still uses stripping at a block level, there is no need for a dedicated hard drive to hold the parity data. This also provides high storage capacity.

RAID Level 5 can allow multiple writes at the same time providing high write and read speeds. On the other hand, RAID 5 is not suitable for transfer of large data files; and when a disk failure occurs, it can greatly affect the system.

In RAID 5, striping occurs at the block level, but parity data is striped along with the disks. The most prevalent RAID configuration, this scheme uses three or more disks, and it can recover from the failure of any single disk at a time

RAID 6

raid-6 | TTR Data Recovery

In RAID 5, striping occurs at the block level, but parity data is striped along with the disks. The most prevalent RAID configuration, this scheme uses three or more disks, and it can recover from the failure of any single disk at a time.

RAID Level 6 is somewhat an extension of RAID Level 5, where there are two parity blocks written in RAID 6 to allow the data recovery process. This is used to avoid data loss in case there is a failure in the concurrent disk, therefore giving high performance for the read operations. It is also good for transfers of large data files.

Contrary to this, RAID Level 6 is not ideal for transferring small data files; also, it requires longer time when writing data because it needs two parity blocks.

RAID 10

RAID 10 Diagram | TTR Data Recovery

This configuration RAID 10 combines block-level striping with two separate parity stripes. As such, it can be used to recover from the failure of up to two drives, and it overcomes many of the problems associated with RAID 5 in larger disk arrays.

RAID 10, also known as RAID Level 1+0, utilizes the combined features of both RAID Level 1 and RAID Level 0. In this level, there is a mirror created for each data block that is likewise stripped.  Because of these features of RAID Level 10, this is considered to have an efficient system to handle multiple drive failures.

Some of the advantages of RAID Level 10 is that the capacity of the disk is moderate and it can store copies of a similar data block. Since it can handle failures of multiple hard drives, it can tolerate system faults and is capable of transferring large data files.

For the disadvantages, it is quite expensive because dual copies will require a double in the amount of the hard disks; and also, there is a need to synchronize the drive spindles.

More About RAID Levels

Raid Fault | TTR Data Recovery

What raid levels are supported by Windows Server 2012 R2?

Windows Server 2012 R2 is the sixth version of Windows Server which added features like iSCSI Target Server, Data Deduplication, Windows PowerShell, Mobile Device Management. and Work Folders. Windows Server 2012 R2 supports RAID levels 0, 1, and 5.

What tools can you use in windows to configure and manage hard drives and raid levels?

To configure and manage hard drives and raid levels using Windows, you can utilize the Disk Management utility software. 

Introduced in Windows XP, Disk Management allows users to look up and manage the disk drives (hard disk drives, optical disk drives, and flash drives), that are installed in the PC, and their associated partitions. A user can use its many functions like partition, format, and assign drive letters, to name a few.

In which of the raid levels are all data lost if one of the drives fails?

Of all the different RAID levels, RAID 0 does not provide data protection. 

RAID 0 provides the benefit of improved performance by employing the data striping technique. RAID 0, however, does not provide data redundancy. So, when one disk drive fails, all data is lost. 

Thus, RAID 0 is best used in applications requiring faster data read and transfer rates; when preservation of data is not a critical part of the operation or a data backup is readily available in case of RAID failure.

Which of the following raid levels yields the largest percentage of usable disk space?

Despite the lack of fault tolerance, RAID 0 yields the most usable space among other types of RAID levels. RAID 0 uses all of the disk capacity and improves the disk I/O by striping data across multiple disks. As data is spread across the disks in the array, simultaneous access to data is possible, which is greatly advantageous especially when dealing with large files.

In a RAID 0 configuration, two or more hard drives are combined and treated as a single, large volume. Thus, a RAID 0 with two 500 GB capacity disk drives will have a combined array size of 1 TB. RAID 0 has no storage overhead which makes it the cheapest RAID level configuration.

What levels of software raid are supported by Ubuntu?

Ubuntu is a free, open-source Linux operating system released with desktop, server, and core editions, with interim releases every six months. Ubuntu server, developed by Canonical, is a server platform for websites, FTP, email servers, file and print servers, cloud services, development platform, and database server.

Ubuntu supports RAID levels RAID 0, RAID 1, RAID 5,  and RAID 6.