Data recovery is possible from a failed RAID 5 array. While data recovery can be complex and challenging with a RAID 5 array, it generally ends successfully. There are several reasons for data loss and the recovery effort for each of them is different. A few examples are below:
Data Recovery with one failed drive
If one drive fails in an array, parity can be used to rebuild the missing data. In this scenario, Ontrack is usually able to recovery 100% of the data. Upon receipt of a non-functional array, the drives from the array are imaged in the clean room. Then the array is virtually rebuilt using those images. Once the RAID is assembled, the file system or volume is scanned for corruption, virtually repaired and the data extracted. The failed drive is often not needed, as any missing data stripes can be rebuilt from parity.
Data Recovery from multiple failed drives
The process is similar to a single drive failure, for recovery from for multiple failed drives. Upon receipt of a non-functional array, the drives from the array are imaged in the clean room. It is important to get as much of each of the failed drives imaged as possible as this allows for the recovery of more data.
Then the array is virtually rebuilt using those images. In the example, Data 2, Data 3 and Parity from stripe one is used to rebuild Data 1. Parity is not needed in the second stripe as all of the data blocks are present. In the third stripe, Data 7, Parity and Data 8 are combined to replace Data 9.
Once the RAID array is virtually reassembled, the file system or volume is scanned for corruption. In addition to file system corruption, engineers are also looking for data that is not consistent or out of date. This occurs when there is a gap of time between drive failures and one of the drives is degraded. Data recovery engineers need experience in recognising this type of damage so they can virtually repair the volume and extract good file data.