this post was submitted on 14 Jun 2024
42 points (100.0% liked)

Selfhosted

40152 readers
570 users here now

A place to share alternatives to popular online services that can be self-hosted without giving up privacy or locking you into a service you don't control.

Rules:

  1. Be civil: we're here to support and learn from one another. Insults won't be tolerated. Flame wars are frowned upon.

  2. No spam posting.

  3. Posts have to be centered around self-hosting. There are other communities for discussing hardware or home computing. If it's not obvious why your post topic revolves around selfhosting, please include details to make it clear.

  4. Don't duplicate the full text of your blog or github here. Just post the link for folks to click.

  5. Submission headline should match the article title (don’t cherry-pick information from the title to fit your agenda).

  6. No trolling.

Resources:

Any issues on the community? Report it using the report flag.

Questions? DM the mods!

founded 1 year ago
MODERATORS
 

I am planning to build a multipurpose home server. It will be a NAS, virtualization host, and have the typical selfhosted services. I want all of these services to have high uptime and be protected from power surges/balckouts, so I will put my server on a UPS.

I also want to run an LLM server on this machine, so I plan to add one or more GPUs and pass them through to a VM. I do not care about high uptime on the LLM server. However, this of course means that I will need a more powerful UPS, which I do not have the space for.

My plan is to get a second power supply to power only the GPUs. I do not want to put this PSU on the UPS. I will turn on the second PSU via an Add2PSU.

In the event of a blackout, this means that the base system will get full power and the GPUs will get power via the PCIe slot, but they will lose the power from the dedicated power plug.

Obviously this will slow down or kill the LLM server, but will this have an effect on the rest of the system?

you are viewing a single comment's thread
view the rest of the comments
[–] [email protected] 17 points 5 months ago (14 children)

The amount of absolutely wrong answers in here is astounding.

NO. PCIE is not plug and play. Moreover, having a dead PCIE device that was previously accepting information, and then suddenly stops, is almost guaranteed to cause a kernel panic on any OS because of an overflowing bus of tons of data that can't just sit there waiting. It's a house of cards at that point. It's also going to possibly harm the physical machine when the power comes back on due to a sudden influx of power from an outside PSU powering up a device not meant for such things.

Why wouldn't instead think of maybe NOT running an insane workload on such a machine with insanely power hungry GPUs, and maybe go for an AMD APU instead? Then you'll get all the things you want.

[–] [email protected] 16 points 5 months ago* (last edited 5 months ago) (11 children)

PCIe is absolutely plug and play. Cards have been PnP since the ISA era. You probably meant hot-plug, but it's hot-pluggable too: https://lwn.net/Articles/767885/

Any buffered data will sit in the buffer, and eventually be dropped. Any data sent to the buffer while the buffer is full will be dropped. I'm not intimately familiar with communicating with GPUs, but I imagine the only buffers are in the GPU driver (which would either handle the removal or crash) or in the application (which would probably not handle the removal and just crash). Buffering is not really where I would expect to see a problem.

That said, a GPU disappearing unexpectedly will probably crash your program, if not your whole OS. Physical damage is unlikely, though I definitely wouldn't recommend connecting two PSUs to one system due to the potential for unexpected... well, potential. Inrush current wouldn't really be my concern, since it would be pulling from the external PSU which should have plenty of capacity (and over-current protection too, I would hope). And it's mostly a concern for AC systems, rarely for DC.

[–] [email protected] 1 points 5 months ago (2 children)

What's wrong with 2 PSUs if both of them are connected to the same ground? I thought multiple PSUs is common in the server space too.

load more comments (1 replies)
load more comments (9 replies)
load more comments (11 replies)