RAID 1 often referred to as a mirrored array provides 100 percent data redundancy by keeping a pair of disks with the exact same data on them, known as mirroring. Although the cost of hard disk drives are low, this type of array is usually only found in enterprise solutions, in particular for high dependency system, which should be kept running 24/7.
The frequency with which this type of array is being seen for data recovery is slowly increasing which is due to a couple of factors discussed below. DiskEng have extensive experience in recovering data from RAID 1 systems where a failure has been suffered by both disks in the array.
Data Safety the Primary Concern
By storing a mirror of the data onto a second disk ensures the highest level of data safety possible with a RAID array. Apart from requiring halving the potential storage capacity, a RAID 1 array has little or no drawbacks over using a single disk, in spite of writing the data to two drives. When reading data it may in some instances produce a small increase in data transfer speeds.
With the price per gigabyte rapidly dropping, it is no surprise that the number of systems using RAID 1 architecture is on the increase, which is one reason for a corresponding increase in data recovery requirements. For high dependency servers this type of RAID may be highly beneficial, but a backup strategy should always be implemented to protect against any potential failure.
RAID 1 Rebuild (Re-mirror)
If a disk in a RAID 1 array fails, the array will remain operational, running in degraded mode. The failed disk should be replaced with a new one, onto which the data from the working drive should be re-mirrored.
Although data transfer speeds have increased, the overall capacity of hard disk drives has also increased, which means that a rebuild can take a considerable time, during which the RAID array is vulnerable. If the two disks used in a RAID 1 array were sourced from the same supplier at the same time, the potential for the second drive to fail shortly after the first is significant. The increased time taken to re-mirror a hard disk is the second reason we are seeing a rise in the number of RAID 1 arrays arriving for recovery.
RAID 1 Data Recovery
Should your RAID 1 array fail, which is usually during the re-mirroring process, it is important not to panic. The two original hard disk drives which comprised the RAID 1 array should be sent for professional data recovery. It may also be beneficial to supply the new hard disk drive onto which the data was being rebuilt, as it may be possible it will hold important data, which may be vital to achieving a successful data recovery.
As long as the hard disk drive which failed first is not too far out of date, it should allow us to use rebuild a fully working array when bad sectors are encountered on the other drive. It is only in the instance of both drives containing the same unreadable bad sector when data loss is likely to occur.