Unraid 5.0 rc16

 

Can I replace 2 disk at the same time with larger disks and rebuild all data from the parity drive?

Unraid 5.0 rc16

 

Can I replace 2 disk at the same time with larger disks and rebuild all data from the parity drive?

No.  It is not possible.    Reconstruction is NOT from just the parity drive... It is from the parity drive in combination with ALL the other data drives.

 

You may replace ONLY one disk at a t time, also, you MUST perform a full parity check AFTER any disk replacement  is completed to ensure you can read what you've just written to it.  You cannot short-cut the process.

If I'm not mistaken, this is the way parity works. Consider the following binary content/value of a bit on each disk:

 

disk1 = 1

disk2 = 0

disk3 = 0

disk4 = 1

Parity = 1+0+0+1 = 2

 

So for example: If you're missing disk2, then all you need to do is to calculate the missing number that would add up to the parity/checksum. The bits can only be ones or zeroes:

 

1+?+0+1 = 2

We're not missing anything, so it must be a zero.

 

 

So in case you're missing 2 variables, then it's not possible to determine the correct missing bits anymore.

If I'm not mistaken, this is the way parity works. Consider the following binary content/value of a bit on each disk:

 

disk1 = 1

disk2 = 0

disk3 = 0

disk4 = 1

Parity = 1+0+0+1 = 2

 

So for example: If you're missing disk2, then all you need to do is to calculate the missing number that would add up to the parity/checksum. The bits can only be ones or zeroes:

 

1+?+0+1 = 2

We're not missing anything, so it must be a zero.

 

 

So in case you're missing 2 variables, then it's not possible to determine the correct missing bits anymore.

 

The example is almost right ... but remember you're adding with a "1-bit" calculator, so the values can only be 1 or 0.  Thus for Parity, you have 1+0+0+1 = 0  (Not 2)

 

So for the missing bit calculation you need to solve  1+?+0+1 = 0

... so for the 3 things you know, you have 1+0 = 1, then 1+1=0 ... so you have to solve 0+?=0, which yields a 0.

 

Note these are for "even parity" (which is what UnRAID uses).    If the parity bit was odd, then you'd want the sum to always be a 1 instead of a 0.