Methods to Recover Data from a RAID 6 Array with Multiple Disk Failure

For enterprises or home users, data is a critical asset. From confidential files to documents and more, we use various storage media to keep our data safe. A RAID 6 setup is one such data storage solution that provides data security and a centralized location for storing data.

However, as a RAID setup consists of HDDs or SSDs, it is very much prone to data loss. Unlike regular data storage devices, a RAID 6 setup uses dual parity to recover data from a failed RAID 6 array.

Let’s dive further to understand more about RAID 6 and how data recovery is performed from a failed RAID 6 setup.

How Does a RAID 6 Array Work?

RAID 6 is a type of RAID setup comprising a minimum of 4 HDDs or SSDs configured in a striped-block configuration for storing data and parity distributed across the drives. RAID 6 arrays work on the Reed-Solomon error correction codes, which are known for automatically correcting data errors.

While RAID arrays are generally known for enhanced performance, the same is not the case with RAID 6. This is due to its complex checksum algorithms and dual parity, which increases the RAID rebuild time, leading to mediocre performance. However, despite its slow performance, RAID 6 has double parity, which results in increased data availability and disk fault tolerance.

Sometimes, a RAID 6 setup also has multiple reserve drives, which are not used in regular functioning and storage. These are kept empty and are used as hot-spares for hot-swapping when an active storage drive fails.

What Happens When a Disk Fails in a RAID 6 Array?

As RAID setups are susceptible to failure, a big question arises: how many disks can fail in a RAID 6 array? The answer to this question is quite straightforward – a RAID 6 array has a fault tolerance of 2 disk drives. If three or more drives fail, the RAID setup completely fails, and the data stored on it is lost forever.

When a RAID 6 array fails, its functionality depends upon the number of failed drives. If there are one or two disk failure, the disk array status changes to Degraded while remaining functional. Data will become temporarily inaccessible but can be recovered after rebuilding the RAID 6 setup.

However, if a RAID setup has multiple disks-failure, i.e., a three-disk failure or more, the array is marked as Failed and the data becomes impossible to recover.

Reasons behind Data Loss in a Failed RAID 6 Array

While a RAID 6 offers increased reliability, data availability, and double parity, unexpected data loss happens. Here are some reasons why data gets lost from a RAID 6 array –

• Failed RAID array
• RAID Controller failure
• Human error
• Absence of RAID partition
• Drive failure
• Disk read/write error
• URE error
• DDoS attack
• Abrupt shutdown
• Power surge/loss

How to Recover Lost Data from a failed RAID 6?

RAID 6 works on the Reed-Solomon codes. If a portion of data stored on an active drive gets damaged or lost, the array controller automatically recalculates and recovers it using complex checksums and parity.

Performing RAID 6 recovery isn’t as simple as it seems. However, it is not impossible either. As a RAID array is a collection of HDDs/SSDs working together as a single storage drive, recovering lost data from a failed RAID array depends upon the number of failed disks in an array.

Simply put, there are 2 cases of disk failure in a RAID 6 array – Single disk failure and multiple disk failure. Let’s talk about these in detail.

Case 1 – RAID 6 with Single Disk Failure

This is the case where a single active disk or drive fails in a RAID 6 array. This is the simplest case of RAID 6 failure as it only requires a simple hot swapping of the failed disk with a hot-spare one. Once the spare disk is hot-swapped, the RAID controller will automatically start rebuilding the RAID array.

However, if a hot-spare disk is not available, the RAID rebuild process can be initiated manually after replacing the failed disk with a functional disk.

Case 2 – RAID 6 with Multiple Disk Failure

In case of a failed RAID 6 array with multiple disk failure, there are two scenarios to look for –

• If two disks have failed in a RAID 6 array, you can use hot-spare disks connected to the RAID to perform hot swapping. Once this is done, the controller will automatically rebuild the failed RAID 6 array and use parities to recreate the lost data. Follow this guide to rebuild the lost data after hot-swapping the drives.
• As RAID 6 has a failure tolerance of 2 disks, a RAID 6 array with 3 disk failure or more will lead to a complete RAID 6 failure. The status of the array will change to Failed, thereby rendering the data present on the drives inaccessible. In such a scenario, failed drives must be replaced with new ones to recreate the disk array and the file system, followed by restoring data from a backup media.

Expert Solution

While rebuilding a failed RAID 6 array is a great way to recover lost data from a failed RAID array. However, improperly swapping the drives or incorrect rebuild can lead to RAID 6 array becoming inaccessible. Controller failure can also lead to data loss from a RAID 6 setup. In such a situation, you can use a RAID recovery software like Stellar Data Recovery Technician.

Using this software helps you perform RAID 6 data recovery in a streamlined manner by first rebuilding the RAID 6 and then scanning the volumes for lost data. Follow the steps mentioned here to perform RAID 6 recovery –

• Purchase and Install Stellar Data Recovery Technician from its official store.
• Launch it.
• On its Home Screen, select the type of data you want to recover. By default, All Data is selected. Click on Next to proceed.

• On the next screen, select the RAID Recovery option at the bottom and click Scan.

• A new ‘RAID Reconstruction’ window will appear. Follow the steps in the given order:
  • Select the RAID 6 tab.
  • In the Select Hard Drives to Reconstruct RAID section, select the missing Hard drives and click on ‘>’ to add them under the Move hard drives up/down for disk order section. You can remove any hard drive at this stage by clicking on the ‘<’ key.
  • In the Move hard drives up/down for disk order section, place the drives in order by using the UP and DOWN buttons present there.
  • Then, navigate to the Select RAID Parameters section and choose various parameters using their respective drop-down menus.

Note – If you don’t know the Parameters, you can select the Don’t know start sector of drives. Show list of probable start sectors’ checkbox. Under it, select a value for Select one or more probable start sectors using the drop-down menu. Similarly, choose the parity order using the Select Parity Order/Rotation drop-down menu. You can also select the Don’t know option.

• Once you have selected all the required values, click on Build RAID. The software will start building the RAID.
• Once the RAID is constructed, you will see it displayed as a single RAID volume on the ‘Selected Constructed RAID’ screen. Select it and click on Show Volume List.

• On the next screen, you will see the list of RAID volumes that the software found after scanning the device. Select a volume and click on Scan.

Note – If the volume is not in the list, you can select the ‘Physical Disk’ and click on Scan to search for lost volumes. You can also perform Raw Recovery in this case. If you are unsatisfied with the displayed RAID 6 build, you can click Reconstruct RAID to restart the RAID rebuilding process.

• Once the Scanning is complete, it will list all the recoverable files. You can preview the files and check their integrity. If satisfied, click the Recover button to save them at the desired location.

Notes –

If you can’t see the required files after performing Quick Scan, you can also perform Deep Scan by clicking the ‘Click Here’ button in the Preview window.

If you are unable to find the required RAID volume/s, you can click on Reconstruct RAID to rebuild the RAID with the correct parameters and perform RAID 6 recovery.

RAID Recovery, Made Simple

RAID 6 is a great setup that offers enhanced data security and availability. It offers data storage and protection for large data sets in a single place. However, its complex dual checksum algorithms result in a lowered read-write performance.

However, even with excellent reliability and enhanced data security capabilities, it is still susceptible to data loss for reasons such as disk failure, controller failure, malware attack, and more. Data lost from RAID 6 can be easily recovered using the methods explained in this post.

A RAID recovery software like Stellar Data Recovery Technician can also come in handy for when you are running short on time and want quick results. We hope the various scenarios explained in this post answered all your queries related to data recovery from a failed RAID 6 with multiple disk failure.

Related Reads

Recover Data from RAID 6 after Controller Failure

Common Symptoms of RAID Array Failure

Introduction to REED-Solomon Codes

FAQs

Q. What to do if a RAID 6 array fails?

A. If there is a single disk or two disk failure, you can rebuild the RAID 6 array by hot-swapping the failed drives. However, if more than two disks have failed, your data is lost forever.

Q. Is RAID 6 good?

A. Yes, RAID 6 is a good option for those who want enhanced data security over performance and speed.

Q. Is RAID 6 slow?

A. Due to double parity and double checksum algorithms for calculating missing data, its read/write operations and rebuild times are slower as compared to RAID 5.

Q. What is the maximum number of drives that can be used in a RAID 6 array?

A. A maximum of 32 disks can be used while building a RAID 6 array.

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About The Author

Keshav Katyal

A passionate writer, driven by his interest in everything tech, Keshav Katyal has always been captivated by the latest gadgets since childhood. His interest in gadgets grew when he got his first gaming console, the Nintendo Game Boy Advanced. Hours and days of tinkering with gadgets encouraged the inner geek in him who now loves writing about the latest technologies.