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I have a Western Digital MyBook Studio II configured into RAID1 (2×1TB) and connected to a Windows 7 machine via USB 2.0. RAID is done through a controller in the enclosure - I've never seen each of the drives separately.

I recently reinstalled Windows from scratch and finally decided to run semi-regular backups. For that purpose, I imaged the pristine install and saved the VHD on the external drive. I then moved it to a different folder on the drive to make sure no backup software overwrites it.

A few days later I noticed something rather peculiar: the VHD file was missing but all other files in that directory were there, but the occupied disk space gauge (and the actual byte values) showed more than the combine size of all files & folders on the disk. I checked this multiple times: made sure that system & hidden files were visible and compared only the 12-digit byte values. The difference is about 40GB, which is about the size of the missing image file. Adding to the strange circumstances, both WD's maintenance utilities (Drive Manager and Data LifeGuard Diagnostics) show no problem whatsoever with either of the 2 HDDs. I tried to recover using a data recovery app but it produced an error message about unexpected MFT records and prompted to check the RAID for consistency.

So how do I check for consistency? And/or how can I trigger the data rebuilding manually?

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The standard Windows CHKDSK is sufficient to check RAID1 and RAID0 for consistency. Other types of RAID usually come with their own utilities that allow parity checks.

In the end the culprit of the missing space story was System Volume Information, which for some reason had unknown data in it despite System Protection being off for that drive.

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