RAID 5 Data Recovery is one of the most popular services provided by service centres since this technology is very popular among server owners. This is due to the fact that RAID 5 has a lot of advantages: higher performance, fault tolerance and relatively low cost of the disk space. The advantages of the RAID 5 are also often exaggerated. In most cases it is considered to be a data storage device, an operating server and a backup at the same time. Such treatment may lead to undesirable effects and cause serious problems, which we will describe in this article.RAID 5 is a set of 3 or more connected hard disk drives constituting a disk system in which the data is stored in blocks. The checksum algorithm, which provides fault tolerance, is recorded in cycles to each hard disk drive equally and according to a certain pattern. Everyone who knows the basic concepts of mathematical logic must remember such simple operations as “modulo-2 addition”. The checksum algorithm is based on this very operation. This algorithm enables fast computing of data stored in the failed disk drive by using data and checksums stored in the other disk drives of the disk array.
Still thousands of people have already faced the loss of data stored in the RAID 5 array. The causes of failure are numerous. First of all this disk system is vulnerable to all logic errors such as deleting, lost or damaged files and folders, damaged file system, virus etc. I think everyone understands that redundancy of RAID 5 doesn't reduce probability of such errors. There is almost nothing special about the disk array as compared to any other storage device. If you know the cause of data loss and if it is deleting, virus, unsuccessful experiments with partition boundaries then the problem salvation method is close to the method of fixing logic errors of HDD or a flash drive. If the problem occurs on the software level it is advised to use data recovery software such as r-studio. It is strongly recommended not to make any changes on the troublesome hard disk drive, not to create, copy or edit data, not to install any software, not to run checkdisk, fsck or other similar utility. Data should be restored to other storage device.
Besides, hard disk drive failure may be caused by external factors. The external disk drive may be damaged by falling or it may burn out. Besides, RAID controller may go out of order. If the motherboard burns out and if the RAID array is connected to it the software RAID, which operates the RAID arrays, will be automatically lost. The problem may be also caused by some temporary defect rather than total malfunction. As a result the RAID array will not properly work though all array parts may not have apparent defects.
Besides sometimes we do unreasonable things like trying to change the position of the hard disk drive in the disk array, resetting configuration of the array, deleting or resetting RAID, repairing it with checkdisk etc. All these actions cause data loss.
Another more classic example of RAID 5 failure is a situation when more than one array members are lost because of their failure or simply because the RAID controller makes them unavailable – off-line. Sometimes it is the HDD that has a defect, sometimes – the RAID controller. Quite often the system doesn’t work properly even though HDDs and RAID controller have no defects at all. The problem may be caused by the sudden power loss or voltage surges.
There are two main methods of RAID 5 data recovery. The first one is data recovery with the help of special software. If all array members work properly, you can connect them to the PC via SATA/SAS/IDE/FC/SCSI or other interface so that each of them will be detected as a separate device. That is there is no need to use RAID controller. If you faced a problem on this stage, it is strongly recommended not to continue.
Implementation of such method is not always possible since you need special technical equipment. To connect 24 HDDs to a single PC so that the OS can detect them as separate devices is not an easy task. It is strongly recommended not to change the data stored in the HDDs, not to initialize them, not to create or format partitions, not to try to access a logical disk. It is better to connect not the original hard disk drive but its sector-by-sector copy. This will prevent unintentional change of data stored on the hard disk drive. Besides you can try various methods without a fear to cause harm to the original HDD.
After you connect the HDDs to the PC, you may use r-studio, UFS-explorer or other similar tools which imitate the RAID controller work and provide access to the data. This method requires creating virtual RAIDs, adding HDDs to the created virtual RAIDs in a definite order, proper configuring of algorithm and setting up the size of blocks.
Thus, you should have experience in the operations mentioned. Otherwise you should practice in RAID Reconstructor. This tool will help you to find appropriate algorithm and pick up a suitable size of the block, provided that the number of HDDs is not large and that the file system used is a common one.
A major drawback of this method is that it is not universal and can be applied to a narrow range of cases. In other words, very few RAID 5 can be recovered with such a method at home. Either RAID Reconstructor fails to find a proper algorithm and the sizes of the block within the available time or such algorithms are not preprogrammed in such utilities or there may be other specific aspects which only a professional knows about.
If such tools don’t provide access to the data, it is strongly recommended to ask professionals for help.
