vardif and rejection rate

[dess]

Hello, this may be a stupid question, since i'm really a newbie, but i'm having a curious problem with my miner. I'm using a 5GH/s BFL ASIC with bfgminer 3.2.1 and everything works ok for a cuple (3-4) of hours, but if i leave it mining overnight i get a ridiculous amount of rejected - stale shares. I'm talking abou 30-34 %, whereas if i leave it on for about 3 hours i have 0.51 % And then after turning bfgminer off and on again i get another 3 good hours. 

I've been trying to get to the bottom of it, and it seems to be caused by vardiff, but that is just my guess.  Is 2.58K/3 a normal difficulty for a 5Gh/s miner? Because i get those, although the rest are usually under 20/3 so that is a big leap IMO. Btw. there are no intensity settings for a BFL SC, i checked and under device managment i can only disable it or view its info, so playing with intensity is not an option. Any help would be greatly appreciated.

[pontiacg5]

2.58k/3 is not a difficulty, but a share that surpasses your current pool difficulty (in this case 3, which is pretty decent for 5Gh.) You will see a lot more shares less than that, most will be closer to 3.

I don't think vardiff is your problem because it looks like the pool is correctly optimizing difficulty based on hash rate. When it starts submitting stale shares do you see higher difficulties (like ###/64, ###/128, ###/256 etc...) That would mean vardiff isn't guessing your hashrate properly, so you won't get anywhere near the shares you can.

Sounds like a hardware/software problem to me, not the pool. Have you tried anything other than BFGminer?

[dess]

Thank you for the explanation. Does that also mean a 2.58k/3 share takes 2579 times more time to hash, than a 1/3 share or am i not thinking about it right?

I think the difficulty setting stays at 3, i just reacted to the first number, because i thought it meant current diff/set diff. I can see i was wrong about that

My second guess was software, because i don't need to restart the device, i just turn bfgminer off and on again and it's working. I haven't tried other miners yet, used bfg just because i knew it supports my asic. I googled that Cgminer should also work ok, so i'll try that. Thank you!

[pontiacg5]

No problem!

All hashes take the same time, you are simply looking for a hash with so many prevailing zeros. The more zeros, the higher the share difficulty. Think of it like a lotto, because that is basically what it is. The more hashes you have, the more chances you have to win.

Vardiff works by tossing all shares below the current difficulty that your machine finds, this saves network bandwidth. The theory is if you have so many hashes available per second chances are enough of them will be high enough to pass the difficulty setting. The pool pays you more for higher diff shares, so in the end you average out exactly the same. You can see how setting diff too high would make a miner run slow then, it doesn't have the statistical advantage of having so many shares at it's disposal, so it won't submit hardly any shares. Vardiff usually sees that and lowers the difficulty automatically.

I prefer Cgminer, but BFGminer plays nice with my block eruptors where CGminer struggles so I use it. Unfortunately that's just how the mining world works still!