RAID Explained

With rapid advances in computer technology and an increased demand for safe, secure and reliable data storage, RAID technology has become a well recognized file storage solution. RAID is an abbreviation for Redundant Array of Inexpensive disks.

What is RAID?
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RAID is a technology that achieves more storage capacity at high speeds, redundancy and fault tolerance by combining multiple hard drives and treating them as a single logical storage unit. Fault tolerance implies the ability of a system to continue functioning as expected even when one or more hard drives fail or otherwise develop an error (fault). Data is copied across multiple hard drives and in the event of a disk failure data loss is avoided. Furthermore, with more hard drives combined the overall system benefits from increased efficiency and heightened performance.

RAID was originally developed for servers to create large storage at lower costs and quickly became popular for hobbyists and home users for many reasons including personal DIY cloud storage and at home media centers.

Different types of RAID

There are several types of RAID arrays and each configuration has distinct pros and cons. The type of RAID array also drastically affects the potential outcome of data recovery and the probability of file recovery success. Let’s talk about the different RAID types to better understand. These are the common RAID types: RAID 0, RAID 1, RAID 5 and RAID 10 (Combination of RAID 1 and RAID 0).


This is also known as a stripe set or striped volume. It's tailored for those seeking high capacities and faster performance. Usually RAID 0 is not recommended for those seeking data security due to its lack of redundancy. As such, it not considered a ‘true’ RAID. It combines two hard drives preferably of identical size and speed to form a single logical volume. This makes it score highly on capacity because the resulting logical “hard drive” achieves twice the capacity. Once installed, data is written across both hard disks simultaneously, thereby doubling movement of data into the storage. In a RAID 0 configuration you are able to fully utilize the capacity of both hard drives. If you are using two 4TB drives, the system only sees one drive with 8TB of space. RAID 0 greatest undoing is that it cannot provide fault tolerance or redundancy. If one hard drive suffers failure or gets corrupted the overall data in its complete state is lost.



Also known as mirroring, this is the first ‘true’ level of RAID and it achieves redundancy and data security by continuously replicating or cloning data across two hard drives in a way that creates a complete backup down to the last bit of data. All data is simultaneously copied to each drive which means the likelihood of data loss is much less. The two drives are cloned, if one drive fails or deteriorates, the other has a complete replica of the data and it can be retrieved or even swapped into service immediately without moving the data. Adding more hard drives will not add more capacity only more redundancy. Unfortunately when it comes to capacity, you can only use half of the capacity available as the other drive is used for replication of data.



This is the most popular RAID type. It’s much more effective in achieving optimal capacity and redundancy. RAID 5 encompasses block level striping with distributed parity. It consists of a system of checksums called parity. If one drive fails subsequent reads can be calculated from the distributed parity in other drives and therefore no data is lost. RAID 5 requires at least 4 drives to achieve its ideal capacity and performance. A single hard drive collects the parity data. In the event that a drive fails, the RAID can be rebuilt and all data recovered. All you must do is add another hard drive to complete the array and begin restoration. The process may take quite some time but is considered a safer option in terms of redundancy and capacity.



This type of RAID array combines the pros of both RAID 1 and RAID 0. Basically, it combines increased capacity and fault tolerance into a single solution. You achieve double the performance and capacity. It’s great when performance and space are concerns while maintaining a budget.


Common causes of RAID failure

RAID systems are generally considered a reliable and safe option for managing and accessing data. However, occasionally they are susceptible to failure just as other hardware devices and this may lead to catastrophic loss of data. The consequences are much more severe if important files were not previously backed up. Remember that RAID is not an alternative for backup and even the most secure RAID array configurations can still fail. With this in mind, it’s imperative to continuously backup your data. RAID may fail due to several reasons, a few of which include:

  1. Failure of RAID controller
    A RAID controller may fail due to a disastrous power surge that can knock out the NVRAM, corrupt your hard drive partitions or damage the boot memory rendering it impossible to boot or access your data.
  2. Failed rebuild of a hard drive
    When a RAID drive is replaced and RAID rebuild errors occur, this may hinder you from accessing your files or even the entire RAID array.
  3. Crashing of the server
    The host machine of your RAID arrays may crash or fail leading to corruption of your RAID controllers and rendering your data inaccessible.
  4. Failure of multiple disks
    Failure of a hard drive in an array may leave your array prone to future disk failure leading to system deterioration. Continued running of the array with degraded drives further increase the odds of suffering an even worse array failure.

What to do when you suffer RAID failure?

So now that you’ve suffered a RAID failure, what are the next steps to take? You’ll need to attempt RAID recovery to get back your data. Generally the safest step at this point is to stop using the array and assess the severity of the damage to your RAID array. While it is generally recommended that you repair and replace the array as needed, recovery may also be an option.

There are several solutions which may help you recover RAID data. There are multiple Windows tools for RAID which can help enable you to recover RAID 0 data that has become corrupted or lost.

RAID 0 recovery

RAID 0 data recovery can be achieved through the following approaches:

Automatic RAID 0 recovery. This approach calls for you to disconnect the hard drive and plug it in to a PC and thereafter use a RAID 0 recovery software tool. It’s a straightforward method that does not require a high skill level. There are many RAID 0 data recovery software tools including both proprietary and free tools. Each recovery software may make use of different options but the concept is generally the same:

  • Disconnect the hard drives from the RAID controller
  • Connect them to a PC one by one
  • Launch RAID 0 recovery software to read the array configuration
  • Feed the controller with the recovered array configuration
ReclaiMe Free RAID Recovery

Sometimes the best option really is the easiest option. Disk Drill for Windows is a popular and well respected recovery tool which is capable of recovering data from individual RAID disks. Disk Drill is a Windows app compatible with Windows 7/8/10 and other modern versions of Windows. While Disk Drill will not repair or recover from the full array at this time it can recover RAID 5 individual files from each disk of the damaged array. Depending on your array configuration this may allow for substantial file recovery even without being able to repair the full array.

    RAID 1 recovery

    It’s possible to recover data from a RAID 1 array even after formatting or deleting the hard drives. In a RAID 1 array setup, data can get lost due to hard drive mechanical damage, drive failure or accidental deletion. You can still recover your data from all those scenarios with exception of physical damage.

    For Raid 1 recovery, you’ll need software just like when recovering RAID 0.
    The basic procedure for recovering from RAID 1 disks and arrays involves 3 basic steps:

    • Launch the software
    • Scan the hard drives
    • Recover files with the software and back them up

    RAID 5 recovery

    RAID 5 Data Recovery is the same as in RAID 0, RAID 1 recoveries, probability varies but there is one additional step specific to RAID 5. The best method for RAID 5 data recovery is to first rebuild your disk array.

    A popular tool for recovering from RAID failures is: Stellar Phoenix RAID recovery. There are quite a few pros and cons to this software which go beyond the scope of this article, however essentially with all RAID recovery tools the probability of success ultimately depends on the original status of the disks and how bad the damage is, in the event multiple disks in an array are damaged, recovery is unlikely for most RAID array types.

    Stellar Phoenix RAID recovery

    Popular RAID Recovery Tools

    Below are the top 10 RAID recovery services recognized by users online. While we have not individually reviewed each of these tools (at this time), these are the most commonly utilized tools for complete or partial (single Disk) RAID recovery.

    1. Disk Drill
    2. EaseUS
    3. Ontrack Easy recovery
    4. DoYourData
    5. R-studio
    6. Amigabit Data recovery
    7. Icare Data recovery
    8. Stellar Phoenix
    9. Secure recovery
    10. Bit Recover

    Disk Drill is a free Windows download, allowing you to scan for free with the Basic Edition. The PRO and ENTERPRISE editions are for enhanced scanning and recovery features and additional data recovery capacity. Getting started is as easy as clicking the free Windows app download (Disk Drill). Once Disk Drill is downloaded, scanning for lost files is as easy as clicking ‘Recover’.

    The probability of recovering RAID 1 arrays is much higher given its mirroring architecture as opposed to RAID 0 where there is no fault tolerance. Other RAID array types have varying success and in all cases individual files (size depends on Array type) can be recovered from each of the disks in a failed RAID array. Disk Drill can scan 300+ file types and features multiple powerful scanning types including Deep Scan which can find files even when the partition table is unavailable, perfect for RAID disk recovery.

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