Much data recovery work involves the salvage of data from one specific type of storage, a hard drive, RAID array, backup tape or DVD. Occasionally a requirement pops up that transcends this norm.
Having faithfully adhered to a regime of nightly backup of a SUN UNIX system, the failure of the hard drive appeared to be an inconvenience that would soon be overcome for this customer. The hard drive having swiftly been replaced, the backup tape was brought back from storage and the restore process initiated. Five minutes in, however, and the DLT drive made a nasty noise, the cleaning lights came on and ufsrestore became ufs-cannot-restore.
We received a call from the customer wanting to know if the data from the backup tape could be recovered. The disk was with another data recovery company who had found that there were a significant number of bad sectors that meant the required data could not be recovered intact. This is not a smug self-congratulatory tale of “then we got everything back from the tape” as at the point where the restore failed there was nothing to be done, that was where the backup had been terminated as the result of a tape problem and no-one had noticed.
The process followed by the customer was to use ufsdump to create a backup file on the hard drive, then to use dd to transfer this to tape. This meant that they had an immediately accessible backup on-line in case of file deletion or corruption, and the fall back of a tape backup to cover against a total failure (or not in this instance).
So, the data could not be recovered from the hard drive nor from the tape, so was all lost? Well, no it was not. An examination of the disk revealed that the ufsdump archive could be partially recovered, but that the critical section at the start of the backup where all of the directory information (which includes slightly important data such as the file names) was lost forever. The tape, however, contained a valid backup up to the point of failure, and an examination of this data showed that it extended into the area of data where files were stored.
In the motor trade a “cut-n-shut” car is viewed as a dangerous beast that should never be allowed on the road, for this customer it was the answer to their UNIX data recovery problem as the data from two sources could be pieced together to create a completed backup and a full restore was initiated.
A happy story, a success, but how often are opportunities such as this missed? The best data recovery service companies, not the biggest but those who understand data, will always pick up on such opportunities to get the right result. But, if the data recovery work is being done by someone who just runs some software and if it says “failed” they move on to the next job then there will be unnecessary data losses.