AHCI passthrough in ESXi

[Patrick Hendriks]

For homelab/NAS purposes I have a 16port LSI HBA with 4x4Tb WD red drives in RAID10 on a X10SDV-TP8F board with 64MB ram.
Esxi boots from a USB, the LSI is in passthrough to the Freenas VM. The MLB sata port are occupied by four 80Gb DC3500 SSD's.
Freenas is installed on two VMDK's (DC3500) in mirror, the other two SSD's are unused.

I am suffering poor write performance (sync writes) in the VM's, so I want to add an SLOG.

This can be done in several ways:
I could add the DC3500 as VMDK to freenas, and make a SLOG this way.

I can also add the two unused SSD's to the HBA, but I do not like this.
I know it is nitwitty, but this would reduce the storage potential by occupying two HBA ports.

This got me thinking. What if I could pass through the AHCI controller?
https://forums.servethehome.com/index.php?threads/esxi-6-0-passthrough-onboard-sata.8902/

I could then install Freenas directly on two DC3500 in mirror (no VMDK) SSD's, and add two DC3500 in (stripe or mirror?) directly for SLOG.
An added benefit is then, if Esxi fails, Freenas could still boot from the DC3500 SSD right? Or am I missing something here?

The issue is then, that VMware still needs a dummy datastore in order to add the Freenas VM. For this I could use a USB drive:
http://www.virten.net/2015/10/usb-devices-as-vmfs-datastore-in-vsphere-esxi-6-0/

Or use the M.2 or mSATA port on the X10SDV-TP8F. However, the manual of the X10SDV-TP8F marks these ports as SATA4-5.
Does this mean they also are in passthough mode when the AHCI is set to passthough? In this case this would not work :-(

Am I on to something or is this completely ridiculous? Any experience? I would like to hear your thoughts. But if there are obvious
reasons to do it in one particular way it would be wasted effort to do it otherwise...

 

[Ericloewe]

Passing through Intel chipset SATA controllers is hit and miss.

One cool thing that should work reliably is passing through a PCI-e SSD. You'd need an M.2 to U.2 adapter plus something like an Intel P3700 in 2.5" form factor.

 

[Patrick Hendriks]

Eric, I'm not sure I understand. Wouldn't an PCI-e SSD, like the a Samsung 950 or 960 pro plugged in the M.2 slot and passed through to Freenas would do the same? I do not get the adapter/form factor part?
This is however a more expensive solution than the AHCI passthrough. I guess that trying is the only way to for for sure.

 

[Ericloewe]

The Samsungs are not appropriate for SLOG. The only proper SLOG devices don't fit on M.2 cards. Many are PCIe card only, with some newer ones being available as 2.5" U.2 (U.2 is just PCIe over a cable).

 

[Patrick Hendriks]

I assume this is because the samsungs lack power loss data retention?

 

[Ericloewe]

I assume this is because the samsungs lack power loss data retention?

Right.