Thursday, 31 May 2012

Group-based filesystems and JBODs.

As of now, there is no automatic recovery of JBOD parameters. At least, I'm not aware of any automatic software that really works.

With a filesystem which stores its metadata all in one place and close to the start of the partition, like FAT or NTFS, you only get the data from the first JBOD member. All the files on the second and further members is lost.

However, with a group-based filesystem, like Linux EXT-series, you can get much of the data by just feeding JBOD members to the data recovery software in turn. In group-based filesystems, metadata is spread evenly across the partition, and file contents are put close to their corresponding metadata. So, if you scan separate JBOD members and then combine the results (skipping empty files and correcting for a loss of folder tree), you can get most of the files out. You cannot recover files which have contents and metadata on two different JBOD members, and also parent-child relationships crossing the disk boundary will be lost. Still, this is much better than NTFS or FAT behavior.

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