I don't know why you keep responding by saying it's not a write-back cache. 1. I didn't ever call it a write-back cache and never even hinted at it operating l

I don't know why you keep responding by saying it's not a write-back cache. 1. I didn't ever call it a write-back cache and never even hinted at it operating like one 2. Write-back caching is only one of many options for write caches Regardless of both of those points, the SLOG ABSOLUTELY will speed up writes if you have a bursty workload (like the virtual machines he's running) and sync=always enabled. >A crucial difference is that the ZIL is limited by the available memory regardless (and tunables, by default 5 seconds worth of data), which would not be the case for a write-back cache device. And yet that point is irrelevant to OPs question of whether or not SLOG was speeding up his writes, which it almost assuredly is doing with the amount of memory and the size of his SLOG device when he is doing sync writes.