FreeNAS Build: Part 1 – Turn on a Power Supply without a Motherboard
After doing much research, I’ve decided to move forward with my FreeNAS build for my home lab\storage. I will be storing VMware datastores via NFS and tons of files via CIFS. The system will be configured (for now) as follows:
- HP DL360G5
- 2x Dual-Core Xeon 3.0GHz
- 32GB RAM
- 4 1Gb NICs
- IBM ServeRAID M1015 flashed to an LSI-92118i
- HP SAS Expander
- Habey ESC-2122C for 12 additional 3.5″ drives
The 12 bay ‘storage shelf’ has already been arrived and reviewed here.
This configuration will put the SAS expander in the storage shelf – so the next question: how to power it?
The HP SAS card only gets power from the PCI-e interface; there is no data connection. So all I need is a powered PCI-e x8 slot – one option is to use a cheap motherboard to power a slot, but never boot into an OS. Another option is having the SAS expander in the actual PC – in my case the DL360…this will not work since I am out of slots (used by the 2nd NIC and LSI SAS card). So with this build, I’ll be using a 2 slot, 1U backplane (PE-2SD1-R10) available here from OrbitMicro.
The only problem with these backplanes is that they do not have a direct means of turning on the power supply – and keeping it on. There are again, a few options – the most common is to jumper the ground and power-on pins – it should be noted that the power button and reset button pins don’t do anything (that I can tell). By jumpering the power-on pin to ground, the power supply is permanently powered on – thus making the external hard switch on the PSU the power on switch. I didn’t like this idea – so I built a circuit based on a 2 coil latching relay to allow the front power button to control the power supply.
Using the 5 volt standby to actuate the 2 coils in the relay – the 2 pin lead is for the built in power button on the chassis and the 3 pin lead connects the ground, +5VSB, and power-on from the backplane.