A redundant array of independent disks, otherwise known as RAID, is a storage technique designed to provide enhanced performance and protection to enterprise data resources. RAID implementations accomplish this with a combination of hardware redundancy and operational techniques that provide varying levels of increased performance and/or protection.
In this article, we are going to take a detailed look at how RAID works, what aspects of RAID storage customers should be most concerned with, and the ramifications of a failure in a RAID array.
How Does RAID Work?
Three basic techniques are used to implement different RAID levels. For some RAID levels, only one of these techniques is employed, while in others they are used in tandem.
Disk striping uses multiple physical disks that act together as a single logical entity. Large blocks of data are broken up and stored across multiple storage devices, providing several advantages.
• Rather than accessing each of the individual underlying physical disks, a process allows them to be accessed as a single logical volume, simplifying resource management.
• Improved I/O performance is achieved by multithreading read and write operations across multiple disks simultaneously.
One disadvantage of disk striping is its low resiliency. If one of the disks fails, it may be impossible to access any of the information stored on the other disks across which the data was stripped. Large amounts of data can be lost unless there is a high-availability implementation with the ability to perform hot swapping.
Disk mirroring is a technique by which data is written to multiple disks simultaneously. It is not, strictly speaking, a backup method, but does protect data by making it available on more than one physical device.
Mirroring provides data redundancy and resiliency. If a disk fails, the mirrored disk can be used immediately with no loss of system performance. This is a vitally important feature for online and mission-critical systems that cannot afford downtime.
An additional important concept for RAID is parity. In parity error checking, redundancy data is calculated for every piece of data written to a disk. The parity data is used with any remaining data to reconstruct the information contained on failed drives. The use of parity error checking requires data to be read and compared from several locations, which can slow down system performance.
What do Different RAID Levels Provide?
When choosing the type of disk storage required by an online system or application, it is essential to understand what features the different RAID levels offer. This knowledge will let you make an informed choice of storage options from your cloud VPS provider.
Here’s an overview of the benefits and costs of the various choices in RAID implementation.
RAID 0 is simple striping across two or more drives without parity. It is best used with non-critical applications that require high-speed read and write performance.
Advantages - Good read and write performance is provided. Disadvantages - No data redundancy meaning all data will be lost if one disk fails. Hardware requirements - At least two disk drives are required.
RAID 1 mirrors data to two or more drives without parity. This level of RAID is good for systems that require high levels of performance and availability.
Advantages - High availability and enhanced data protection are provided. Disadvantages - Duplicating data across multiple disks increases hardware costs. Hardware requirements - At least two disk drives are required.
RAID 5 employs disk striping with distributed, interleaved parity. It does not use a dedicated parity disk. This level of RAID offers protection in situations where the number of drives is limited.
Advantages - The array can withstand the failure of a single drive with reduced performance. Disadvantages - The array will fail if there are two disk failures. Hardware requirements - At least three disk drives are required.
RAID 6 uses dual distributed parity with disk striping. It’s good for long-term data retention and business-critical applications.
Advantages - The array can withstand the failure of two drives. Disadvantages - The array will fail if there are more than two disk failures. Hardware requirements - At least three disk drives are required.
RAID 10 combines RAID 1 and RAID 0 with no parity. RAID 10 is good for minimizing downtime and addressing heavy I/O requirements.
Advantages - The array can withstand the failure of multiple drives. Disadvantages - This RAID level requires additional disk drives. Hardware requirements - At least four disk drives are required.
RAID 50 combines the distributed parity of RAID 5 and the disk striping of RAID 0.
Advantages - Better write performance, increased data protection and faster rebuilds are achieved with RAID 50. Disadvantages - This RAID level requires additional disk drives. Hardware requirements - At least six disk drives are required.
What Types of Problems Impact RAID Arrays?
RAID arrays can experience complete or partial failure for several reasons. When an array fails, the best practice is to stop using it until the issues are resolved.
• A RAID controller is used to direct the operation of the array. The controller can fail due to power surges or other issues. This problem can cause various problems with the RAID array including the inability to boot the system.
• Missing RAID partitions can be caused by corrupt disks and stop working correctly.
• Incorrectly rebuilding a RAID volume can result in data access issues or a full RAID failure.
• Multiple disk failures can cause the complete array to fail. Running the array with a failed disk in degraded mode increases the risk of a total failure and should be avoided whenever possible.
• A crash of the host server can make the array inaccessible.
The size of a drive is the major determining factor in the time needed to rebuild it in case of failure. Failure to promptly address drive failures and allowing the RAID array to operate in a degraded manner exacerbates the problem and will lengthen the time required to fix the system. Large and complex RAID arrays can take weeks or months to successfully rebuild.
Do RAID Arrays Need to Be Monitored?
The simple answer to the above question is “Yes.” Without a proper monitoring strategy, you risk data loss and degraded system performance. You can use dedicated software tools provided by the manufacturers supplying the hardware to construct the array. More general monitoring solutions that provide the required visibility into the physical and logical disks that form the array are also available.
Monitoring should be performed by the team responsible for implementing and managing the RAID system. In the case of cloud-hosted dedicated servers or virtual private servers (VPS), your provider will usually handle this task to ensure your data is always available and protected.
What are Atlantic.Net's RAID Offerings?
Atlantic.Net has multiple RAID implementations available for their dedicated hosting and VPS hosting customers. Here are some of the flexible storage options they offer.
Dedicated cloud host customers can choose from the following plans.
• SATA SSD RAID1
• SATA SSD RAID10
• NVMe SSD RAID10
• Fully customizable storage is available, allowing customers to implement any level of RAID they need.
Customers opting for a VPS solution for their cloud hosting needs enjoy the data protection and performance of a highly redundant RAID 10 storage architecture. Even when individual hardware components fail, data will remain accessible and optimal system performance will be maintained, enabling your business to keep operating productively.