September 4, 20232 yr Hello, first post this, and great to be here. I finally settled on Unraid for my home server/NAS system. I don't have hardware yet, because there are still some issues that need to be resolved, some of which I hope to resolve in this forum. This is the first one. I plan on going all-in with a 7 x SATA SSD RAIDZ pool, with one disk worth of parity, so this would already be quite fast… fast enough (on paper) for my stage #1 NIC solution (dual SFP+) to be a bottleneck. Almost all of the motherboards I've looked at offer an option to add at least one gen4 M.2 SSD, either directly, or via OCuLink or SlimSAS or PCIe 4.0 slot (carrier card) etc., which would be even faster than the ZFS RAID, i.e. future-proof for a later NIC upgrade to SFP28, so my question is, whether an Unraid setup that uses ZFS and RAIDZ would need both an L2ARC (metadata-only!) and a dedicated M.2 SSD for the traditional Unraid cache, e.g. for application data/metadata. Would two caches be a reasonable option, or be redundant? Nota bene: I know that ZFS is still fairly new in Unraid (stable), and I faintly remember reading that enabling L2ARC currently isn't possible yet in the UI, so I don't know if enough of you have even tried this.
September 4, 20232 yr 5 minutes ago, eicar said: and a dedicated M.2 SSD for the traditional Unraid cache, e.g. for application data/metadata. Note that if using a raidz pool then in the current release a cache drive is not relevant for that purpose as you can only cache writes to the main array, not to a pool. This restriction is expected to be removed in the 6.13 release although we have no ETA for that. having said that you may well want to use the SSD as an application drive for best performance of docker containers and VMs.
September 4, 20232 yr Author Thank you for the quick reply. I do plan on using quite a lot of Docker containers, but no VMs—I'm even thinking about disabling Intel Virtualization via BIOS to save power. 😉 Your answer kinda supports my gut feeling that (at least with enough RAM) ZFS already has a good amount of ARC as read cache, so you can probably do without an L2ARC, while a fast gen4 M.2 SSD would be a good option for Unraid application data. Edited September 4, 20232 yr by eicar
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