Although RAID 1, also known as a mirrored array, employs 100 percent data redundancy to provide a high level of fault tolerance, it does not guarantee against a failure of the array. With the price of hard disk drives tumbling over the last decade, RAID 1 is now starting to become more common outside its traditional stronghold of the enterprise market. It is however still most commonly found in high dependency server systems where continuous 24/7 operation is required.
The factors which have led to a steady increase in RAID 1 systems requiring data recovery are discussed below. At DiskEng we have seen a wide range of RAID 1 systems arrive for data recovery, usually as a result of a failure to both disks in the array, adding to our vast knowledge of this type of technology.
Fault Tolerance the Main Objective
The use of a mirrored pair of hard disks provides the highest level of fault tolerance available using the current technology. RAID 1 technology has only a single major drawback, in that the potential storage capacity is only half of the total disk capacity used. This is a minor concern for anyone requiring a high level of fault tolerance and in some cases such a configuration can allow the data transfer speeds to be increased by small margin, over the use of a single disk.
It is little surprise that the uptake of RAID 1 arrays has increased as the price of hard disk drives has decreased, the biggest single factor leading to an increased requirement for data recovery. This type of configuration is essential for high dependency servers, where uptime must be assured, but it is important that backup strategy is also implemented to guard against a potential failure of the array.
RAID 1 Re-mirror
A RAID 1 array will continue to operate in degraded mode following the failure of a single hard disk. Once a disk fails, it is essential that it is replaced with new drive. The data contained on the working drive should then be re-mirrored onto the new disk to restore the maximum level of fault tolerance.
Until the rebuild process has completed, the RAID 1 array will continue to operate in degraded mode, during which time it is vulnerable to any failure of the remaining working drive. Although data transfer speeds have risen dramatically, so has the capacity of drives, meaning that in many implementations of a RAID 1 configuration, the rebuild time has not decreased, but increased when some of the largest drives have been used. This is the second factor which has resulted in an increase in failed RAID 1 systems arriving for data recovery.
Data Recovery from RAID 1
Most RAID 1 arrays fail during the re-mirroring process, when an unreadable bad sector is encountered on the drive from which the data is being re-mirrored. If this happens, you should not panic and make an attempt to recover the data yourself, as it may result in additional damage. The best solution is to send the pair of hard disk drives for professional data recovery. You should also send the drive onto which the data was being re-mirrored, as we have found in some cases it has contained data which has proved to be beneficial in successfully recovering the data from the RAID.
In most cases, both drives can be used to rebuild a complete copy of the data replacing any unreadable bad sectors using the data from the second drive. If the first drive failed and was not replaced, the data contained on it may be out of date, which will affect the quality of the data recovery possible and may complicate the process. In most cases data recovery is fairly straightforward, with data only lost when the same sector on both drives cannot be recovered.
