Hi
I've been doing Windows Server from some time now, however when it came to storage ZFS is what I lately used. This job requires native Windows storage and WSS and ReFS quite look like MS' answer to ZFS and BTRFS on the unix-ish side. Sine single/double parity seem to have very poor endured write performance mirrors are the only thing I'm looking at.
I've done the following test in a VM and became surprised with the resulting space:
- The future server would have 10 disk slots available for storage (12-Slot chassis, 2 Slots for OS)
- I created a VM with 10*5GB VHDs
- I've read about The "NumberOfColumns" value, creating a mirror it creates a Virtual Disk (VD) with 5 Columns
Here are the numbers of space:
- 10 * 5GB -> 50GB, utopic size
- Usable space per after initialization: 4.87GB per disk -> 48.7GB
- Simply creating a pool with these 10 disks: 42.5GB capacity, Free Space 40GB (already 8.7GB lost)
- Creating a fixed, maximum size mirror VD: 15GB /!) -> Add 5GB of loss again
- I could create another extra fixed, maximum size mirror VD: = new 3GB virtual disk
There are a couple of things that confuse me more or less, and I haven't found a calculation scheme to get some data in advance for resulting available space:
- Why is an empty storage pool losing 8.7GB of total capacity even before creating any VD?
- Why can't I create just 1 VD with the full available capacity (42.5/2= 21.25 GB) but only 15GB and then create another one?
I know that both WSS and ZFS use some space on the disk to write the pool configuration data, this does add up (on ZFS we have things like ZFS intent log or ZIL etc.) but I not understanding how on earth I'm ending up with a loss of 33.7GB of "wasted" space which ends up with a 30% usable space for the largest VD?!