This is a good question. The guidance I had been given was between 4-8 SSDs per JBOD tray. I’ve just found guidance that is a bit more precise. This is what Microsoft says:
When purchasing storage for a tiered deployment, we recommend the following number of SSDs in a completely full disk enclosure of different bay capacities in order to achieve optimal performance for a diverse set of workloads:
| Disk enclosure slot count | Simple space | 2-way mirror space | 3-way mirror space |
| 12 bay | 2 | 4 | 6 |
| 24 bay | 2 | 4 | 6 |
| 60 bay | 4 | 8 | 12 |
| 70 bay | 4 | 8 | 12 |
Minimum number of SSDs Recommended for Different Resiliency Settings
This is great information that has been notoriously difficult to come by. In fact there is almost no communication anywhere on how best to layout a tiered storage space. Or even where to start. I ended up settling on 8 SSDs in a 24 bay DataOn JBOD in a 2-way mirrored space, and am very happy with the performance.
Note – Not all SSD’s (SAS SSD’s) will work for clustered tiered storage. Check they have the correct firmware level
What SAS SSD’s (make / model) do you guys use for Storage Spaces?
Also, if we’ve got 3 JBOD trays for redundancy, set up as a 2way mirror – do we “have” to use 4 SSD’s in each tray, or would we get away with 2?
And what would be the downside of only using 2 in each JBOD?
We use HGST SSDs from the DataOn Storage HCL. We tried SanDisk, but they have a bad habit of shipping out of date firmware and not sharing their firmware publicly on their business products site. And I’ve also heard that they have a high failure rate.
Having only 2 SSDs puts you into a 1 column scenario with the entire virtual disk, which greatly reduces performance.
Is this a per JBOD requirement, or just an overall recommended HDD to SSD ratio ? I’m trying to set up a 3 JBOD (60 bay), 2 head node cluster right now. I’m using only 56 HDDs and 8 SSD spread over the JBODS and went happily to work. However the combination of enclosure awareness and a 4 column two-way mirror gives me a “not enough eligible disk error” on the SSD tier.
Yes. Sounds like you have enough for 2-way 2 column virtual disks. Double the SSDs per JBOD and you can do 4 columns.
Ok, I’m feeling dumb here. Are you telling me I can do one 2-way 2 column disk pr head node (as I’m expecting) or just the one to share (which is bad design).
If the latter then what the heck am I thinking wrong? 🙂
I have 8 SSDs:
(2*2 = 4) + (2*2 = 4) = 8 SSDs and should Work? Or to keep it simpler just one 2*4 = 8?
Using the GUI with a 4 column default on the pool estimates a whooping 8 GB capacity on the SSD tier. My raw SSD capacity is 760 GB :/