Since THIS thread has gone quiet, I thought I'd try to start a new thread and see if it gets any takers.

I'm running Windows Server 2012 R2 Essentials, all patched up.

I have a storage pool which contains 4x4TB USB3 and 1x2TB USB3 drive.

I have a thinly provisioned parity instance, set to 16TB, which thinks it's using 10TB of the pool.

Though the (non-Essentials) Server Manager reports it's usage slightly differently at 6TB:

But I'm guessing some of that is due to slabbing and parity.

Mean while, the volume itself reports that it's only using 4TB:

So I've tried to do an Optimize-Volume f -ReTrim -SlabConsolidate -Verbose to get back what appears to be over zealous slab allocations, but after a couple of days, it's still sitting on 0%:

CPU usage is sitting around 40-50% for the defrag process (dual CPU machine), but disk activity is basically zero for the volume being analysed.

1. Am I doing the right thing to retrieve space in my storage pool?

2. How did Windows let the storage space get this bad?

I had the weekly defrag turned on/automatic, but this looks like it's never succeeded.

3. Without buying more disk, creating a new storage pool, moving all the data across and deleting the old storage pool, how am I going to dig myself out of this?

Thanks
Craig

3.1 And if I do have to move everything off, what's to stop this from just happening again?