Litecoin GPU mining: pool reports a much lower hashrate than cgminer

[pennytrader]

cgminer shows that my 5830 gave me 320khs but the pool site only shows about 170khs. I have tried different pools btw.

anybody else seeing this?

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[Vuxil]

Pools tend to be kind of inaccurate because of latency and stuff imo, my pool-reported hashes per second always tends to be a little higher or lower than what I read locally

[pennytrader]

I know

Pools tend to be kind of inaccurate because of latency and stuff imo, my pool-reported hashes per second always tends to be a little higher or lower than what I read locally

I surely know that. But as I said, it's MUCH LOWER (and yes, I had my miner running for more than 24 hours. And the rejection rate on my client is very low!)

[eiswuerfel]

I have atm the same problem. Cgminer shows me 310kh/s and notroll.in only 78kh/s

[pooler]

The cause of this is most often hardware errors.
cgminer checks every solution generated by your GPU, and if one turns out to be incorrect because of hardware errors it (rightfully) doesn't even submit it. Since pools can only estimate your hashrate based on how many solutions you submit in a given amount of time, their estimate will be lower than your real raw hashrate. This raw hashrate, which is correctly displayed by cgminer, is, however, not meaningful if the solutions your card generates are wrong.

You need to make sure that all of the HW figures in cgminer are zero or next-to-zero; if that's not the case, you need to review your settings.
Remember that scrypt mining puts a lot more stress on GPUs than Bitcoin mining, so you don't want to push your hardware too much.

ADDENDUM. Reaper behaves differently, as it doesn't check for hardware errors and just submits every solution your cards find. All wrong solutions will however be counted as invalid and not be paid by the pool, and you may well get banned if you keep submitting mostly invalid shares. The worst part is that many newcomers don't realize that it is not fine to have a high invalid ratio.
Also to be noted is that some pools take both valid and invalid shares into account when estimating your hashrate, so if you use Reaper the estimate provided by the pool may match the speed reported by the miner even if most of your shares are invalid. I have seen neophytes switch to Reaper just because the speed reported by the pool was higher than with cgminer.