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How many disks does RAID One require?

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A RAID 1 creates an exact copy (or mirror) of a set of data on two or more disks, so you need at least 2 disks. You can read this for more.

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RAID 1 also requires an even amount of drives. If you want to use an odd number (like 3 drives) you need RAID 1E. – Ƭᴇcʜιᴇ007 Mar 17 '11 at 18:22
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I think it would be wasteful to use it with any more than two drives, as you lose half your storage space. Using a parity level like RAID-5 would be better, or RAID10 (or RAID0+1), which gives you speed as well as mirroring. – paradroid Mar 17 '11 at 18:34
    
while I'm sure it depends on the raid controller, you might use Raid1 with >2 disks (over Raid5/10/0+1) if you were worried about being able to access the data in the event that you lose the raid controller (ex: HW failure + no replacement) – Xantec Mar 17 '11 at 19:34
    
So harddrives and two other hard drives? – jack Mar 17 '11 at 21:05
    
Yes, one harddrive (source) and two other harddrives to be used for RAID 1. – Mehper C. Palavuzlar Mar 18 '11 at 17:22

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