As described in this thread an ECC Memory overclocking (link) I plan to set up a RaidZ2 with dedup for scientific data and some VMs on my home workstation (covid issue – can’t get to university)
For the dedup I will for sure need L2ARC: The question is what SSD best to use on my Asus WS x570 ACE (the 3 x8 PCI-e solts are populated with two GPUs and a HPE 240 HBA — the latter is connected via the x570 chipset as you can see here (link). )
I (realistically) have 3 possible connections available:
var 1.) via the second m.2 nvme slot (this is x2 PCI-e 4.0 via the x570 chipset) with the system SSD in the primary slot
var 2.) via the primary m.2 nvme slot (this is a x4 PCI-e 4.0 slot directly to the CPU)
var 3.) via the HPE 240 after purchasing a SAS-3 expander (i.e. via the x570 chipset)
(I do not want to use the U.2 connector cause I want to plug a 10G ethernet in there via this (link) adapter)
Nothwistanding my future plan to use this as a NAS box I do not need it in th emoement but only lan to use it locally also for VMs.
My question is: What variant of SSD connection would you recommend and what SSD for the scenario.
Would for example a simple PCI-e 3.0 SSD via the secondary m.2 slot (with x2 lanes) be sufficent for L2ARC when wanting to practically use it for VMs?
Would it be better to use the first m.2 slot with a PCI-e 4.0 SSD and put the system SSD in the secondary slot?
Or screw that all and go SAS-3 SSD? If so - is there any budget option 
you could recommend?
I personally tend towards var 1. and later upgrading to var 3.
Looking forward to your thoughts on the subject.
Thank you very much for your input 
