I think write-through cache means they always write to both, but they try to fulfill reads using the faster device. https://en.wikipedia.org/wiki/Write_through

I think write-through cache means they always write to both, but they try to fulfill reads using the faster device. https://en.wikipedia.org/wiki/Write_through_cache#Writing_policies https://en.wikipedia.org/wiki/Write_through_cache#Writing_po... With a write-through cache, writes are slow, but the cache is never stale. With write-back, writes can be faster, but the caches can be incoherent. I have LVM2 set up to use my SSD as a cache for my spinner. I think it's write-through mode. Maybe.