What is the minimum number of SSD drive for a tiered + mirrored storage spaces volume?

Question

Does Windows Server 2016 (or Windows Server 2012 R2) allow the creation of a Tiered Mirrored Storage Spaces volume with the following configuration:

• HDD tier: 2 HDD same size, mirrored (RAID 1)

• SSD tier: 1 SSD drive

For example, I have 2 x 136 GB HDD and 1 x 250 GB SSD that I want to set up as a single volume of 386 GB (136 GB + 250 GB) in such a way that the HDD is protected through RAID 1 but the SSD is not mirrored. I can then use the SSD for Write-back cache and to store hot data through the Tiered feature of Windows Storage Spaces technology.

So the questions are:

1. Whether I can have just 1 SSD even though there are 2 HDD?
2. If this is not allowed in Windows Server 2012 R2, please indicate whether it is allowed in Windows Server 2016.
3. If this is not allowed via the New Virtual Disk wizard, but allowed through PowerShell script, can you provide the commands to create the pool + virtual disk?

Answer 1

1. You'll need at least 3 disks in each tier to build storage spaces, and at least 4 if you're looking to build a decent mirrored space of HDDs.

2. This is how it looks like even in WS2016

3. No overrides via powershell available.

This is something you can still do with a hardware RAID & Cachecade/Flash cache utility.

Answer 2

A simple answer is "No". You would need minimum 2 SSD disks for mirrored-tiered storage spaces.

I've had a similar concern when during the deployment of three-node Storage Spaces Direct, it happened that I cannot use LRC (erasure coding, basically). For some reason, Microsoft only supports LRC starting from 4 nodes while other guys (Simplivity, Starwind, etc) can do this starting from 2 nodes. Sad but true :(

Answer 3

For Two-Way Mirror and Single Parity with write back cache you cannot use single drive in the SSD tier.

https://technet.microsoft.com/en-us/library/dn387076(v=ws.11).aspx#bkmk_wbc

Simple answer: three times no :-)