Windows finds only 1 disk, 454 Gb but I have RAId problem

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Polypheme
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A RAID array (of 2 HDD units) will appear to be only ONE "disk" as far as Windows is concerned.

The message you are getting is IMPORTANT, so pay attention. If a drive in a RAID array fails, you lose ALL your data! So make sure to do a complete backup of your data as soon as you can. THEN you will need to find out which unit is failing and replace it. This will mean completely making a new RAID0 array with the replaced unit installed, and then restoring all your backup data to the new array.