RAID level: the most important RAID concepts compared

Combining hard drives as a RAID has various advantages and disadvantages. These cannot be generalised since the specific properties of a network depend on the selected RAID level. Each level is different, depending on how many hard disks are combined and which methods are used to store the files.

We explain how RAID levels differ and what the effects of the different approaches are. Our comparison of RAID levels also shows how each performs in terms of cost, reliability, and performance.

RAID levels such as RAID 5 or RAID 6 describe different approaches for connecting hard disks in a network that functions as a single logical drive. When RAID technology was first presented in 1988, the idea was to save costs by combining disks in a hardware cluster. Today, the cost factor barely plays a role and is only considered when evaluating between the various levels.

The decisive properties in which RAID levels differ from one another today are as follows:

• Degree of resilience
• Read speed (output rate)
• Write speed (input rate)
• Utilisation of available storage capacities
• Minimum number of hard drives required

The primary goal of RAIDs is to increase the security of stored data. Failures of individual hard drives are compensated for and data loss is avoided. To this end, individual RAID levels employ different techniques to store files redundantly. The classic procedure is, for example, the mirroring of all data whereby information is duplicated in a disk cluster. Alternatively, other RAID levels rely on parity information that is stored together with the user data on the integrated data carriers and – in case of a defective storage medium – helps to restore data quickly and easily.

To boost performance, many RAID levels make use of striping, a process whereby the stored data is broken down into strips and distributed evenly across all integrated hard drives. In this way, both the write and read speed can be optimised – the degree of increased performance depends on the chosen redundancy method.

Compared to individual drives, many RAID levels offer both increased reliability and improved performance. However, the following rule of thumb applies: the higher the fail-safety of a network, the weaker its performance improvement.

The maximum storage capacity users have available for their data depends on the methods used for redundancy. RAID levels that rely on mirroring data only have 50 percent of storage space available. Where parity is used in a RAID, the storage capacity increases with the number of hard disks.

The relationship between fail-safety, performance, storage capacity and ultimately also the cost differs from one RAID level to the next. Some approaches such as RAID 0 and RAID 1 are designed for a single purpose. While RAID 0 ensures increased data throughput when reading and writing, RAID 1 focuses on the duplicate storage of files and thus only a minimal improvement in read speed is achieved (with a suitable RAID controller).

The table below compares the properties, strengths, and weaknesses of common RAID levels.

For many years, RAID systems were the ultimate in saving data in a more fail-safe and performance-boosting manner. However, plenty of alternative technologies now exist.

Multi-copy mirroring is a practical RAID alternative whereby – as with mirroring in RAID level 1 – several identical copies of the data are created. In contrast to a RAID system, however, these copies are on different hosts in the network and include a mode that continuously checks the status of the data. If this recovery mechanism encounters damage or inaccessible data, it is immediately repaired using a copy. The number of copies is determined by the user, with each copy always taking up as much storage space as the original, which makes MCM a rather expensive proposition.

Erasure Codes use algorithms that break down data into subsets or blocks – just like the striping method as in RAID levels 0 or 5. The individual data parts can be conveniently distributed to separate storage locations. Erasure codes also have a checking mechanism that ensures the readability and availability of the data. The RAID alternative requires additional storage space of 33 percent, which makes it one of the most cost-effective options for file backup. Erasure codes are best suited to storing large data sets, as the division into blocks is particularly efficient here.

We’ve already touched on the fact that a RAID should never be used as an alternative to a backup and similarly a backup shouldn’t be misunderstood as an alternative to a RAID. Backups in the cloud serve the sole purpose of storing data in a separate location. Improving reliability or read or write speeds aren’t the aim of cloud storage. However, as long as hardware optimisation isn’t your goal, cloud backup solutions are a good option for securely storing your data.