Emergency RAID Recovery Services

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RAID 10 Rebuild Failure

“On return to the office on the Monday morning, we were horrified to find our RAID server had gone offline, with no option to rebuild the array. Many thanks for the hard work in recovering our data.”

N Patel, Bracknell

A failed RAID array, containing four 4TB Western Digital hard disk drives arrived at our laboratory from Bracknell. The drives were examined, revealing no hardware or electronic faults. Sector-by-sector images of all four drives were secured by our data recovery specialists. Two of the drives were found to have approximately a dozen unreadable bad sectors during the imaging process.

Each hard disk is designed with an additional space which is used to swap out bad sectors as they are encountered on a drive, for which a list is maintained. This list is however, only of a finite in size, which means it will in time be used up, after which all new bad sectors become apparent to the operating system, or RAID controller. When a set of hard disk drives is maintained within the same environment, and also sourced from the same supplier, each drive will tend to develop bad sectors at a similar rate, making it likely that the swap area will be exhausted at a similar time.

The drive images were examined revealing a RAID 10 configuration, known as a striped mirror set. This means that the presence of bad sectors on a drive will only cause data loss if the same sector within a mirrored pair can not be recovered. Our data recovery specialists created a virtual RAID 10 set, which when examined revealed a single unrecoverable sector. The single unrecoverable sector contained the first Master File Table entry, used to mount the single 8TB NTFS volume. Fortunately, a second copy is stored on the volume, allowing our engineers to overcome the loss and recovery all of the 3.6TB of data files which were returned to the client.

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