That wouldn't add fault tolerance. In fact, it would increase the likelihood of failure - because you'd be putting more stress on the physical drive.
this post was submitted on 27 Jul 2025
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It won't work with RAID because you need drives of the same general size, but you could make a mirror of the NVME onto the other drives I suppose. I don't see any benefit to this though. It kinda sounds like you're creating a solution to a problem that doesn't exist here. You also probably won't see any performance benefit to using the 500GB as a read cache for a number of reasons, so maybe consider if you absolutely and desperately REALLY wanna use those two slots, just buy two drives and make a volume out them. Simplifies your setup quite a bit.
Could you elaborate on why the read cache won't work? I'm aware of the high RAM requirement, and plan to allocate 40GB to the L2ARC. Or is there some other bottleneck I'm not aware of?
These things are expensive, so I'd appreciate any info.
My thought process for the mirroring is that in the event the nvme fails, the pool will remain accessible, just extremely slow in comparison to previously, and it'll be easier for me to replace than if I just made regular backups to the primary storage pool.
I won't write a novel, but using L2ARC for anything is pretty pointless unless you're doing constant reads on multiple large objects at once, and you're consistently transferring them. More memory is always the first thing that will improve performance, partially because it's just faster, but also because the filesystem you're going to be running on (especially ZFS) already does its own caching, which is faster/better.
If this is just a home setup, and not something serving a database or video editing workspace, you won't get any real benefit from dedicating an entire SSD to just caching.
Thanks for the info! I didn't realize that ZFS already does caching. I guess I'll use those two nvme slots for two identical drives for my secondary pool then.