Low ETH hashrate on R9 280x

[Malacsult]

I just tried out ETH mining on my Sapphire R9 280x

I saw that other people are getting over 20 MH/s out of their R9 280x, but I'm only getting around 13 MH/s, why could this be?

At first I tried it on MinerGate, but then I moved over to ethermine.org, the results only slightly
improved.

My CPU is an FX-8320 (Windows 7 64bit)
Both my CPU and GPU are overclocked, but they're very stable as they are.

I'd really appreciate any suggestions!

 

[TMTOWTSAC]

You running the latest AMD drivers?

 

[Malacsult]

You running the latest AMD drivers?

I am, yes (17.6.1)

 

[TMTOWTSAC]

Looks like over time as more currency is mined, the size of the work units (DAG I think) increases, and starts to require more VRAM. As it gets closer to the limits of the cards VRAM, it mines slower and slower. Once it exceeds the max VRAM, it won't mine at all. Saw references to it calling it the "DAG memory thrashing bug" and googling that got me this discussion:

https/www.reddit.com/r/EtherMining/comments/6hfivj/hd_7970_hash_rate/

Seems 12-13 MH/s has very recently become normal for 3 GB VRAM cards, and soon they won't be able to mine ETH at all.

 

[Malacsult]

Looks like over time as more currency is mined, the size of the work units (DAG I think) increases, and starts to require more VRAM. As it gets closer to the limits of the cards VRAM, it mines slower and slower. Once it exceeds the max VRAM, it won't mine at all. Saw references to it calling it the "DAG memory thrashing bug" and googling that got me this discussion:

https/www.reddit.com/r/EtherMining/comments/6hfivj/hd_7970_hash_rate/

Seems 12-13 MH/s has very recently become normal for 3 GB VRAM cards, and soon they won't be able to mine ETH at all.

Thank you very much, now I understand why

 

[Malacsult]

Looks like over time as more currency is mined, the size of the work units (DAG I think) increases, and starts to require more VRAM. As it gets closer to the limits of the cards VRAM, it mines slower and slower. Once it exceeds the max VRAM, it won't mine at all. Saw references to it calling it the "DAG memory thrashing bug" and googling that got me this discussion:

https/www.reddit.com/r/EtherMining/comments/6hfivj/hd_7970_hash_rate/

Seems 12-13 MH/s has very recently become normal for 3 GB VRAM cards, and soon they won't be able to mine ETH at all.

Probably a very dumb question, but...

Can you use your DDR RAM when GDDR runs out to speed up?

 

[TMTOWTSAC]

Pretty much no, system RAM is used by integrated video, but dedicated cards have their own, faster (and more expensive) VRAM such as GDDR5 or just recently HBM and HBM2. System RAM is usually DDR3 or DDR4. It wouldn't be worth the added cost to GPU makers to include a second memory controller to use slower system RAM.