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How to Rebuild a Failed RAID without Losing Data

In our computer technology age, digital information became an all-important, crucial value. Images, music, videos, documents, emails — daily we deal with large amounts of data being operated and stored on our devices, and those quantities increase significantly when it comes to business processes needs. RAID (Redundant Array of Independent Disks) hard drives were invented and put into practice as one of the ways to suit those requirements by offering increased performance and data loss prevention while not causing bottlenecking as the previously used methods would do.

However, there’s no perfect solutions. If you are in the unfortunate situation when your RAID array has failed or is running in degraded mode – read the article below to learn the ways of rebuilding it in a proper manner. Once you make out how a RAID hard drive works, there are a few steps you can take to avert stored data loss.

Considering Configuration

It is necessary to grasp there are many RAID array types (or levels), each of which has its own set of redundancies — and hence divers fault tolerances. Thus and so, before making decision on what should be accomplished in your case, it will be helpful to get a little background information on those differences.


Based on a striping technique, it is also known as “stripe set”: RAID 0 uses two or more disks in order to improve server performance. However, failure of one hard drive disk in this configuration means the whole array being affected — which is why you won’t be able to rebuild it.


This configuration applies disk mirroring technique where two or more disks mirror one another to prevent data loss. By copying data from one disk to another, it creates a mirror image of the information and a built-in copy of everything the user has done. During the initial mirror build, there is always a bit of lag in computer function — but the speed goes back to normal as soon as the procedure is accomplished. RAID 1 is used where system reliability is critical.  


Such type employs both striping and parity techniques to improve performance and reduce information loss. With disks arranged in a RAID 5 (from 3 and up to 8 units), one hard drive can temporarily go offline and no data will be lost that way — which means that in the event of corrupted, or otherwise damaged drive, RAID 5 will continue to operate in a degraded state. RAID 5 recovery is more complicated, but the information can still be recovered if one of the disks has failed. This array is most often used in companies and enterprises.


Very similar to RAID 5, but utilizes two different parity functions. In spite of the fact its recovery is very complex, RAID 6 is able to survive more than one hard drive failure. 

RAID 10 (0+1)

This array is based on mirroring and striping techniques, so that it inherits RAID 1 fault tolerance and RAID 0 speed efficiency. Such configuration is able to survive a single disk failure and, in some cases, get over multiple simultaneous hard drive failures as well. RAID 0+1 is one of the most expensive types, because the capacity overhead increases with a number of disks.

Rebuilding your RAID

Rebuilding a RAID is necessary when one disk of the array stops working, even if it does so temporarily and everything seems to be functioning correctly: with a hard drive going offline, workload put on others becomes enhanced as they have to perform tasks instead of the defective one — ergo, it’s only a matter of time when the still-working hard drives are going to suffer the same fate. If that happens, data recovery will become a difficult (and almost impossible) thing to accomplish.

Here are a few strong recommendations to follow throughout the process of RAID reconstruction if you need your data to be saved:

●  Before rebuilding your array, create a RAID structure image, as well as a backup on a separate volume. These actions will secure your data immediately before restructuring.

●  Do not create a new RAID on old drives! That will ruin the newly-created array and all your previous data.

●  If you can’t access and/or backup all the data stored in your RAID, do not attempt to rebuild it, contact the data recovery experts immediately. However, if you can back it up, do it first and fast to avoid total information loss. Any failed rebuild attempts lower the chances of successful data restoration.

●  Until the data is fully restored, you must be careful in all your actions: do not create, copy, move, append, delete or save any files on the disk as that can lead to overwriting data on a damaged disk — as well as opening of bulky programs and applications.

●  Rebuilding a RAID is a quite complicated and nuanced task to do; performing repairs on your own may cost you all the important information stored on the disks. In case you are not completely confident in your technical skills, it will be much wiser to delegate the rebuilding to a Data Recovery specialists.

●  Do not remove more than one disk simultaneously from its initially installed position because you may lose track of the sequencing of the drives. Labeling the drives and the matching slots as you removing them should help.

●  Do not ever ignore any RAID subsystem failures warnings or any malfunctions.

This guid should help you to rebuild a failed RAID. Act according to the following steps:

1. Determine and secure the current state of an array; label the drives, wires, cables, ports, controller configuration, etc.

2. Disconnect the array member disks and connect them to the controller which is capable of working with separate disks (it can be either a non-RAID controller or a RAID-controller in single drive mode).

3. Launch a RAID Recovery Software and recover the array parameters.

4. If the RAID monitoring application and controller allow you to build the array without initializing it, then try to do so in this mode according to the parameters determined by the RAID Recovery Software. Be very cautious in case you are attempting this, because if the array is rebuilt with wrong disk order, the data will be lost.

5. In case of a hardware RAID, you can write the array to the disk and then try to mount the disk in whatever operating system was used. If you don’t have a disk that is large enough, then you can build a temporary array and write data on it. Anyway, never write any data to the member disks of the original array.

6. Once your information is saved and checked (always open at least several large files to be sure that data is reconstructed properly), rebuild the original RAID and copy data back. 

How long does a RAID take to rebuild?

In general, RAID rebuild time depends on two things: the quantity of data being calculated and the capacity of the array itself; smaller RAID can be rebuilt in just a few hours, while more complex ones can take well over 24 hours.

Need help or have questions about your failed RAID?

SALVAGEDATA’s data recovery service experts have been completing RAID recoveries for individuals, 500 companies, and federal institutions all across the USA. So, don’t hesitate to contact our RAID recovery help service line at 800-972-DATA (3282) for immediate assistance — day or night!