Storage Spaces Direct Calculator PREVIEW

Choose Your Drives

Indicate what drives will be present in each node, excluding boot devices.


This results in 0 TB of physical capacity and 0 TB of cache per node. ?

If devices of multiple types (NVMe, SSD, or HDD) are present, the fastest are automatically used as cache. Each faster device binds dynamically to several slower devices, to accelerate I/O for consistent low latency. These devices do not contribute to the overall capacity, since everything stored in cache is also stored elsewhere. To learn more, check out our documention here.

You have chosen devices of 0 type(s). There will be no Software Storage Bus cache.

Choose Your Scale

Indicate the number of nodes in your cluster.

Based on your chosen fault tolerance, the following deployments are possible. Choose one.

Choose Your Resiliency

You can use three-way mirroring or dual parity. Choose how much of your data you'd like to store using each. ?

Mirroring provides faster access to data, but is not as capacity efficient. Parity incurs some computation time and cost to encode/decode data, but is more capacity efficient. For more details, see our documentation here.

The proportions of your tiers are fixed by the capacity of your SSD and HDD devices.

To use parity encoding, you must have at least 4+ fault domains. Consider scaling your cluster. ?

Parity encoding stripes data and parity symbols across fault domains to densely and efficiently store infrequently accessed data.

At large enough scale, it can achieve 80.0% efficiency without compromising fault tolerance. (Compare with just 33.3% efficiency for 3-Way Mirroring.) It requires at least 4 fault domains. Consider scaling your cluster to unlock parity encoding.





Storage Efficiency: ?

Mirroring has efficiency. Using only mirroring would give available capacity.

At this scale, dual parity uses encoding which has efficiency. Using only parity would give available capacity.

Combining these in the proportions you've chosen gives overall.

Excludes reserve.

Usable Resiliency Reserve

Reserve: ?

This deployment has total physical capacity, excluding cache.

We recommend setting aside the equivalent of one capacity drive per server, up to 4 drives, for in-place recovery. This guarantees an immediate, in-place, parallel repair can succeed after the failure of any drive, even before it is replaced. In this case, that's drives x each. See our documentation here for more information.

This leaves total physical capacity after reserve.


This app is still in development. It is being tested on Chrome 51+ and Edge 25+.

For feature requests, bug reports, or general feedback email Cosmos Darwin.