ELI5: why two 2.5" drive bays on the TrueNAS Mini-X and Mini-X+?

[SoonerLater]

ELI5 (explain like I'm 5 years old) what is the purposes of the two 2.5" drive bays on the TrueNAS Mini-X and Mini-X+?

The five 3.5" drive bays will obviously be filled with 3.5" spinning HDDisks. The two 2.5" drive bays can fit 2.5" spinning notebook drives (but nobody would do that, right?) or 2.5" Solid State Drives. And I assume that SSDs are the intended occupants for the smaller drive bays... but what would you do with them? The SSDs wouldn't be in the same pool as the 3.5" drives, right? And you wouldn't just make a mirror of two SSDs, would you? Is there some way to make the SSDs be some sort of super-cache for the main pool?

Confused.

 

[HoneyBadger]

And you wouldn't just make a mirror of two SSDs, would you?

Why not? With SATA SSDs being widely available in 2T/4T capacity, that's a huge amount of fast storage.

Is there some way to make the SSDs be some sort of super-cache for the main pool?

Yes; SSDs can be used as:

• Second-level read cache (L2ARC) to provide faster-than-HDD access to a subset of data that's too large for RAM
• Separate LOG device to accelerate sync-write workloads (SLOG) - note that I didn't say "write cache" as it only helps that specific workload
• Special devices in a TrueNAS Fusion Pool (special) for holding pool metadata or files below a certain size threshold

special devices can also be used for dedup but please don't just toggle that on without doing some serious research first