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Date: Wed, 3 Mar 2021 14:37:47 +0100
From: Solar Designer <>
Subject: reusing mining GPU rigs (was: Implementing mixed mask attack)

On Wed, Mar 03, 2021 at 01:57:50PM +0100, Micha?? Majchrowicz wrote:
> BTW since now bitcoin miners are buying GPUs by pallets

More like Ethereum miners.  Bitcoin is effectively ASIC-only for years.

> I heard it's good idea to buy used hw that often they often sell (at
> reasonable price) when switching to newer cards etc. Is this
> reasonable to buy something like that or is it just "a fairytale" ? :)

This is tricky.

If you want the cards to run reliably for years, you'd want so-called
reference design cards (horizontal fins, only one blower fan) and
expensive chassis.  That's not what miners use, so also not what they
eventually sell.  However, if you're OK with opportunistic use (make the
maximum use of cheaper used GPUs until some of them die), then
re-purposing GPUs formerly used for mining might be more cost-effective.

Also, if you buy an entire mining rig, it will likely be an open air
frame (as required for non-reference design cards with vertical fins to
be reasonably cooled) rather than a chassis, it will likely use flexible
PCIe extenders passing only 1 PCIe lane to each GPU, and it will likely
use a cheap/small motherboard+CPU with little RAM (and perhaps a lower
maximum RAM size than you could have in a "proper" system).

Whether this suits your needs or not depends on a lot of things,
including the type of (non-)hashes you would be cracking and what
implementations for those exist - e.g., some of our OpenCL formats do
everything performance critical on device, but some others use a mix of
host and device code - thus, some would be fine with 1 PCIe lane and
slow CPU, but others would be hurt by that.

Then latest GPUs are a lot faster and more energy-efficient for many
uses... but not a lot for many others.  When a miner upgrades to newer
GPUs and sells old ones, this probably means the old ones are no longer
cost-effective for their mining.  Which means they also might be no
longer cost-effective for password cracking, or on the contrary the
specific password cracking task might be different enough that they're
still a good choice for it.  Or a specific miner's reason to sell might
be different (e.g., they quit mining for whatever reason, not upgrade).

Miners run the GPUs 24/7, so they care about electricity costs a lot.
You might expect to run your password cracking jobs sporadically, and
if so you wouldn't care as much.  (But you would probably care about the
heat anyway.)

So it's all about the detail of the specific offer and how it fits your
needs (or does not).

I do know someone who bought former mining rigs for password cracking.


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