Understanding raidz1 available storage

[GruenSein]

Hello all,

it seems, I have a some trouble grasping the inner workings of an inhomogeneous raidz1 pool. Until recently, I had a setup with 5 disks (2x 2TB and 3x 1TB) running FreeNAS 11.0-U2. All was working well until one of the older 1TB hard drives started posting SMART errors and unrecoverable sectors, which prompted me to replace it. As I had another 2TB drive left over, I used this drive to replace the misbehaving one according to the procedure described in chapter 8 of the documentation. Resilvering went flawlessly. The only thing that I am a bit confused about is that the pool capacity has stayed the same at approx. 5TB. My understanding is that it should have increased to 6TB (sum of all but one drive which can provide the parity for all other drive. In this case, a 2TB drive). Following the documentation, I tried to detach the pool and reimport it for the system to recognize the added capacity. Unfortunately, this did not work. Am I missing something? Or is this behavior to be expected?

I am grateful for any hint or input. All the best!

 

[danb35]

Or is this behavior to be expected?

Yes, it is. When you have a RAIDZn vdev consisting of varied disk sizes, the size of the smallest disk controls. So, whether you have 5 x 1 TB disks, or 4 x 8 TB and 1 x 1 TB disks, the capacity of the vdev would be 4 TB (less ZFS overhead, etc.).

 

[nightshade00013]

Also even though you have multiple 2TB drives you still have some 1TB drives in play. To grow the pool like what you are thinking ALL the drives will need to be at least 2TB.

Basically what you had was:

2TB 2TB 1TB 1TB 1TB = 5TB storage minus 1 parity disk for approx 4TB available total storage.

Now you have:

2TB 2TB 2TB 1TB 1TB = 5TB storage minus 1 parity disk for approx 4TB available total storage.

Basically the smallest disk in a pool sets the maximum storage the pool can handle.