Date: Wed, 3 Mar 2021 14:37:47 +0100 From: Solar Designer <solar@...nwall.com> To: john-users@...ts.openwall.com 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. Alexander
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