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I usually mine only, when I do stuff using my PC so it is on anyway. So far I used Slushs Pool but they have a score based reward system, which seem to punish casual mining. If a long round ends >15 minutes after leaving the pool (due to shutdown the system) you'll probably get nothing at all. What are better payout models for the casual miner and what pools can be used?

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There are multiple approaches to pooled mining, each with its own benefits and detriments. Assuming you are a dedicated miner who does not pool hop then the scenario you describe should be an "edge case" that should rarely if ever occur. That said, common payout schemes include:

  • PPS - Pay Per Share. Each submitted share is worth certain amount of BTC. Since finding a block requires shares on average, a PPS method with 0% fee would be 50 BTC divided by . It is risky for pool operators, hence the fee is highest.
  • SMPPS - Shared Maximum Pay Per Share. Like Pay Per Share, but never pays more than the pool earns.
  • ESMPPS - Equalized Shared Maximum Pay Per Share. Like SMPPS, but equalizes payments fairly among all those who are owed.
  • CPPSRB - Capped Pay Per Share with Recent Backpay.
  • Prop. - Proportional. When block is found, the reward is distributed among all workers proportionally to how much shares each of them has found.
  • PPLNS - Pay Per Last N Shares. Similar to proportional, but instead of looking at the number of shares in the round, instead looks at the last N shares, regardless of round boundaries.
  • Score - Score based system: a proportional reward, but weighed by time submitted. Each submitted share is worth more in the function of time t since start of current round. For each share score is updated by: score += exp(t/C). This makes later shares worth much more than earlier shares, thus the miner's score quickly diminishes when they stop mining on the pool. Rewards are calculated proportionally to scores (and not to shares). (at slush's pool C=300 seconds, and every hour scores are normalized)

The important factor is that you avoid Proportional payout systems as they are vulnerable to pool-hopping so you will probably lose some portion of your revenues to hoppers on those pools. For your concerns, SMPPS, ESMPPS or PPLNS would be good choices, but there are other factors to consider and it is ultimately up to you to choose a payout scheme and pool that best fits your needs.

  • Having only an 5670, I received 0.0+0.0+0.0004 btc for mining 2.5, 3 and 4.5 hours. With increased difficulty this can be even worse. So much for the "edge case". – mbx Sep 1 '11 at 16:12
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    True, I hadn't considered miners so slow (or rounds so fast) that they may not submit any shares in a given round. Mr. Schwartz may be correct in choosing PPS for such a scenario. I suppose as someone pushing 3 GH/s I need to revisit my definition of "casual miner" before making a judgement call. Still, for anyone with even a single 5830 or higher my advice still holds. – David Perry Sep 1 '11 at 16:14
  • See answer below--size of miner doesn't actually impact the fairness of score-based mining, only the variance. – eMansipater Sep 2 '11 at 15:45
  • It does if the size is extremely small. While CPU miners are almost nonexistent these days, mining at 1-10 MH/s only submits a share every several minutes. If a user has only a few shares per round their placement can make or break profits in any scoring method that involves time in its calculations. With a 5670 the OP should be pulling ~70 MH/s which is obviously above this threshold, but the lower your hashrate the more noticeable the effect can become. Better for low-hashrate miners to move to something like PPS and take luck out of the equation entirely. – David Perry Sep 2 '11 at 15:50
  • Wow, I never imagined the models to be this complicated. I thought you're just ... getting paid your fair share of hashing power per X blocks. – ripper234 Sep 2 '11 at 17:55
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Flat pay-per-share may be best. These tend to have the highest percentage fees, but the payout is 100% predictable. There are a few PPS pools, such as abcpool.co and btcserv.net with no fee. The only thing they keep are the transaction fees, so your payout per submitted share is 50 divided by the current difficulty.

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It's a common misunderstanding that score based reward systems like Slush's underpay infrequent miners. While it's true that shares in a given round devalue if you mine towards the beginning of a round and then leave long before it finishes, you have to also take into account the fact that the length of a round is random. So you have equal chances of arriving late in a round and having your shares worth more than they would have been by straight proportion, or starting out a round and having it find a block right at the beginning (making each share worth a lot more because there were fewer of them). In the long run, these all average out perfectly.

The only circumstance in which you will be receiving less from a score based pool is if you consistently start out rounds but then switch to other pools when the rounds "take too long" for your liking. You can't do this by accident. It's a specific attack that we identified and analysed back in January, and unless you specifically program a miner that does this it's not going to happen consistently by random chance.

That said, there is a slight difference with the score based system for very low-capacity, infrequent miners: increased variance in your payouts. Sometimes they will be bigger than normal, and sometimes smaller. Mathematically, it all ends up coming down to the fee you pay, but psychologically this might be hard to take as sometimes you will feel ripped off, while you might not notice that you also get lucky just as much. So it might be easier on your brain to go with a pay-per-share system or similar, it just won't be easier on your pocketbook.

The biggest underlying problem with this is that you probably shouldn't be mining at all. Even if you only use it when your computer is on anyways, a 5670 almost certainly draws more power when mining than you earn back in bitcoins, unless you're paying very low electricity prices (5 cents or less per kilowatt-hour) or using someone else's electricity (in which case all you're doing is taking money from them, not earning it). Probably it's time to leave the mining to high-efficiency rigs located in very low-cost electricity zones.

For a complete analysis of different mining pool schemes, Meni Rosenfeld has written an excellent paper.

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