If the RAID has failed (from corrupted meta data or multiple failed member disks for example) then it is advisable to recreate the original configuration of the RAID. You’ll likely need to image the healthy member disks, repair any that have failed, determine the RAID parameters and then configure and mount a virtual RAID. You may not need to go through all of these four steps, but there is software that will do them all if required.
Because you’ll be attempting to resolve the problems by yourself, you need to create an exact image of the disk so that if anything goes wrong then you always have a copy of the original data. Performing a sector-by-sector copy allows you to preserve file structure and other data so that you can attempt recovery on the disks without causing further permanent damage.
You should always be cautious when trying to image data on a disk that is failing, especially if it’s a mechanical error. By attempting to access the data you could cause more physical damage. It might be better to avoid the risk and simply send the disk that has failed to the professionals who will then be able to image it for you. If it’s a logical fault then you may have some luck with a disk repair or partition recovery tool which will allow you to repair the disk and then image it.
In creating a virtual RAID you will need to know the specific parameters from the RAID that has failed. This means that the disk order, block size, block order and offset all have to be correct else the virtual RAID will not mount since it won’t be recognised as valid. Some software will try to detect the values automatically, but it’s not always successful. The best way, although a bit more complicated, is to follow this RAID recovery tutorial in order to find out the parameters manually.
When all of the above is complete, you can go about building and mounting a virtual RAID. Mounted, the volume can then be used to run data recovery practices on it as if it were a single disk. Some data recovery software will let you do this in the program.
Data can be successfully recovered from failed RAIDs if you’re using a quality piece of software. Although you may have to shell out a bit of cash for the right one (although nowhere near as much as you would for a professional company), especially have the ability to rebuild your RAID included, it’s worth it if it does the job and gets your data back.