RAID Storage: Levels & Common Failure Causes Explained

Filed Under: Resources

If you’re reading this then possibly either your RAID system has failed or you’re wondering whether RAID is fail-proof. RAID systems are, certainly, robust and provide fault tolerance. But that doesn’t mean RAID arrays are failure-proof.

RAID (Redundant Array of Independent Drives) combines two or more hard drives into a single logical unit to increase the performance and/or reliability of data storage. This technology distributes data across the drives in one of several ways, referred to as RAID levels.

The RAID system can also be deployed as hardware (consists of controller card or chip) or software (software-only or hybrid). Whether you choose hardware or software, RAID is available in different schemes, or RAID levels, such as RAID 0, 1, 5, 6, and 10.

All these RAID levels differ in terms of redundancy and performance. Depending on the RAID level, an array uses techniques like Striping, Mirroring, and Parity. Depending on your specific needs, you can choose a RAID level that suits you best. You may also use a RAID Calculator to compare different RAID configurations and determine how much capacity you need.

Different RAID Levels

Originally, there were five standard levels of RAID, but over the years many variations including nested and non-standard levels have developed.

  • RAID 0 – striping
  • RAID 1 – mirroring
  • RAID 5 – striping with parity
  • RAID 6 – striping with double parity
  • RAID 10 –mirroring and striping combined

RAID stores the same data on multiple hard disks to offer superior performance and reliability. It means that if one or multiple disks fail, your data can still remain safe. However, this fault-tolerance feature doesn’t give 100% protection against RAID failure and data loss. Whether you’re using RAID 5 or 10, in the worst scenario, your system may report a RAID drive failure. Your RAID server array may suffer multiple RAID drive failures or something more complex.

When it comes to RAID system failure, you may find several RAID repair software applications on the market. But most of these software applications are ineffective in cases where hardware has failed or broken down. That’s why only specialized RAID recovery services offered by data recovery professionals help in RAID data loss cases.

What Causes RAID Failure?

The most common causes of RAID Failure include:

  • A Failure of the RAID controller
  • Missing RAID Partitions
  • Failed Rebuild of RAID Volume
  • Multiple Disk Failure
  • Server Crash
  • Fire or water damage
  • Virus corruption

Now, let’s take a closer look at different RAID levels to find out what makes them vulnerable to failure and data loss.


The most basic level, RAID 0 is the most efficient in performance. However, this simple two-drive configuration doesn’t offer the best data protection and fault tolerance. RAID 0 is used primarily for expanding capacity and speed but lacks data redundancy capabilities. This setup does not protect your data by making an additional copy. So, even if a single drive fails, the user can suffer complete data loss. If one drive encounters a mechanical or logical issue, the RAID data recovery professional will need to repair or rebuild the system.


RAID 1 also uses two hard drives but it uses a mirroring technique in which data written to one of the drives is automatically copied to the other drive. The mirroring technique creates an identical pair of drives and provides data redundancy to RAID 1. So, if one drive fails, the mirroring can save the data. In the case of RAID 1, data loss occurs when all drives fail. If one drive has failed and you keep using the system, the other drive will have to bear the extra load and this may result in a second drive failure. So, if you don’t act immediately when one drive fails, there is a high chance of second drive failure and data loss. Another possibility is both drives failing simultaneously due to age, physical damage, natural disaster, or excessive wear and tear.


With a minimum of 3 drives, RAID 5 uses a combination of data striping with parity to achieve better performance and higher data redundancy. This technique distributes data across multiple drives and that means that RAID 5 can withstand one drive failure without experiencing data loss. But it will not protect your data in the event of a second drive failure. So, continuing to use RAID 5 in a degraded state will lead to an entire array breakdown. Besides multiple drives failure, RAID 5 can also malfunction due to controller failure or partition loss. RAID partition loss is often a result of a virus attack that can corrupt the header of a RAID partition and make it disappear. You may also encounter this issue due to incorrect RAID rebuilt, power surge, hardware or software errors, or bad sectors.


Both RAID 5 and RAID 6 are somewhat similar with the difference that RAID 6 uses two parity blocks per stripe to increase fault tolerance. The use of two parity blocks means that RAID 6 can tolerate up to two drive failures without data loss. The use of an additional hard drive increase capacity of RAID 6, as well as offers more protection. The problem may occur due to RAID controller errors after RAID rebuild when a new drive is incorrectly added to the array. Replacing failed drives also puts pressure on the remaining functional drives and that makes RAID 6 susceptible to failure during a rebuild. Moreover, if the hard drives are of higher capacity, the rebuild process will take more time and that will make functioning drives more vulnerable to failure.

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