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What size does the parity drive need to be?

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This isn't clearly spelled out anywhere that I could find. Say I have 7x500gb drives. Would a 501gb drive be enough for parity if it existed?

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It has to be as big (or bigger) than the largest data disk. With all 500G data drives, a 500G parity is perfect.

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I was surprised you'd have trouble locating this very basic piece of information about unRAID, but when I looked I did not immediately find it either.

 

Here is a description of how parity works in unRAID.  It will help you understand why the drive doesn't have to be any larger than the largest drive.

 

There have been a few reports of certain motherboards / disk controllers "hiding" a very small amount of space on a disk drive.  This can result in, for example, 2 500G drives being of slightly different sizes.  Although this is pretty rare, it has caused some users consternation as unRAID will not accept a parity drive smaller than the largest data drive, even if the size difference is tiny (even 1 sector would be too much).

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I have problems like that with raid controllers in the past.. They should all round the drive sizes down a little to some acceptable figure..

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I have problems like that with raid controllers in the past.. They should all round the drive sizes down a little to some acceptable figure..

 

The Areca's have a configurable option to do this.

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