L2ARC and SLOG on the same device ?

[metebalci]

Is it possible and OK (disregarding some performance implications) to use the same device as L2ARC and SLOG ? Particularly I am talking about a P4800X and the installation is for home use, not many users and not much load. I know L2ARC is optional, means additional RAM usage and might be unnecessary and SLOG is only for sync-writes. I only wonder this in terms of possibility because when L2ARC and/or SLOG is needed, it might be impossible to have two different hardware (limited number of PCIe/NVMe/SATA).

 

[jgreco]

The system won't set that up for you automatically, and some stuff like I/O reporting and disk replacement of the misconfigured SSD will be broken. Underneath it all, though, yes, you can theoretically do it. It's generally a better idea to get a properly sized mainboard instead, though.

 

[HoneyBadger]

Just to build upon the reply from @jgreco - the performance hit against an Optane device in this (unsupported) configuration will be significantly less than conventional NAND SSDs, as they don't suffer the same hit to transfer rates or latency under a mixed R/W workload.

 

[metebalci]

Very helpful thank you. This made me think, if there is a very limited performance loss, if I run TrueNAS virtual, then I can do this from the host and then would I/O reporting etc. function normal ?

 

[jgreco]

To run TrueNAS virtually, you would need additional I/O capacity on the virtualization platform in order to support the hypervisor boot and hypervisor datastore to hold the TrueNAS VM. This means you would be using a larger platform. So just go and do that larger platform, and then run TrueNAS on the bare metal. Then, yes, everything would function normally because you wouldn't be trying to cram ten pounds of crap into a five pound bag.

 

[metebalci]

Not sure if I understand you 100% correct, but I already have an Epyc virtualization platform running other things, and still have plenty of resources including I/O. I am considering both options: building something new for baremetal TrueNAS or virtualizing it on this platform. Although I dont prefer to have hdds locally (have zero hdds at the moment there), it is also simpler and cheaper as I already have considerable resources here, so I started to consider this more seriously.