What is RAID?

RAID (redundant array of independent disks) is a setup consisting of multiple disks for data storage. They are linked together to prevent data loss and/or speed up performance. Having multiple disks allows the employment of various techniques like disk striping, disk mirroring, and parity.

In this article, learn the types of RAID, the pros and cons for each, the difference between hardware, and software setup of multiple drives.

guide to raid levels and types

RAID Levels

Depending on the techniques used, there are four (4) common types of RAID:

Additionally, you can decide on the way to implement RAID on your system. Therefore you can choose between hardware RAID and software RAID.

RAID 0

RAID 0 is also referred to as disk striping. The technique includes dividing data evenly across two or more storage devices (HDD or SSD). The purpose is to speed up performance as organizing data in such a way allows faster reading and writing of files. Disk striping is the best solution for large applications with enormous amounts of data.

RAID 0 is the most affordable type of redundant disk organization and is quite easy to set up. However, such an arrangement is not fault-tolerant or error-free and should not be used for critical data. Since it does not use data redundancy, problems on any of the disks could result in complete data loss.

RAID 0 example with disks

Advantages of RAID 0:

  • Increased read and write performance
  • Full capacity use, no overhead
  • Easily implemented

Disadvantages of RAID 0:

  • Not fault-tolerant (no redundancy)

RAID 1

RAID 1 (disk mirroring) is fault-tolerant as it duplicates data by simultaneously writing on two storage devices. Therefore, each disk has an exact copy on another disk. This technique does not include parity or striping, meaning the data can only be as big as the smallest disk.

Having a RAID 1 setup ensures protection against data loss. If a problem arises with one disk, the copy provides the data needed. It also speeds up performance and availability as it allows systems to read simultaneously from both disks. Still, writing takes more time as it only uses the capacity of one disk and has to operate twice.

RAID 1 with disk 1 and 2

Advantages of RAID 1:

  • Increased read speed
  • Fault-tolerant
  • Doesn't require data rebuilding (if a driver fails, data is simply copied to the replacement driver)
  • Easy to implement

Disadvantages of RAID 1:

  • Uses only half of the storage capacity
  • More expensive (needs twice as many drivers)
  • Requires powering down your computer to replace failed drive

RAID 5

RAID 5 uses disk striping and parity, creating the most popular choice for organizing independent disks.

Raid 5 requires a minimum of three (3) disks on which data is striped, but not duplicated. As protection against disk failure, it uses parity spread across all drives to rebuild data if needed. This makes it highly reliable even in the event of data loss.

RAID 5 provides high performance and reliability. Not only is it secure, but it also does a good job balancing reads and writes. It also uses the space of an entire disk to store parity, reducing the aggregate amount of data users can save.

How RAID 5 works diagram with 4 disks

Advantages of RAID 5:

  • Fast read transactions
  • Consistent access to all data
  • Fault-tolerant

Disadvantages of RAID 5:

  • Uses only half of the storage capacity
  • Requires more time to rebuild data (at least one day up to a couple)
  • Parity overhead that causes lower performance rates
  • More complex to implement

RAID 10

RAID 10 combines RAID 0 and RAID 1 with a minimum of four (4) disks.

The setup of two (2) disks are striped, they are also mirrored on two (2) other disks, creating a single array of disk drives. Such a configuration benefits from RAID 0’s high performance and RAID 1’s fault-tolerance.

In the case of disk failure, RAID 10 provides fast recovery thanks to data redundancy. This does come with a price though. This technique is more expensive and complex to setup compared to other RAIDs. In addition, it essentially uses only half of its storage capacity.

RAID 10 example with 4 disk types

Advantages of RAID 10:

  • High performance
  • Fault-tolerant
  • Fast rebuild time

Disadvantages of RAID 10:

  • Costly (requires more storage capacity)
  • Limited scalability

Hardware RAID VS Software RAID

There are two ways of utilizing RAID, differing by where the processing takes place. If the RAID processing occurs on the external CPU, it is hardware RAID. If it can also take place in the host server’s CPU, it is software RAID.

When installing the hardware setup, you insert a RAID controller card in a fast PCI-Express slot in the motherboard and connect it to the drives. External RAID drive enclosures with a built-in controller card are also available.

For the software setup, you connect the drives directly to the computer, without using a RAID controller. In that case, you manage the disks through utility software in the operating system.

In this article, we only deal with the hardware setup of RAID, using the LSI MegaCli tool on CentOS/RHEL Based Distros.

Conclusion

RAID is a useful and practical way to speed up server performance and ensure that no data is lost. Deciding what kind of setup is best for your business greatly depends on your priorities. Explore all the options and get all the advantages of this powerful tool and techniques.