On February 21, 2Miners began receiving initial reports of a considerable decline in the performance of Antminer E3 mining rigs while mining Ethereum Classic (ETC). The report revealed that some clients had experienced a six-fold decrease in hashrate on the Bitmain Antminer E3, from 180 MH/s to merely 30 MH/s. Subsequent investigations revealed a sudden overall drop in hashrate on all the ETC cryptocurrency mining pools.
The 2Miners team speculated that the cause in this decline was associated with the growth of the DAG (directed acyclic graph), a file produced after every new set of 30,000 blocks referred to as a mining epoch. During the mining of ETH, a GPU requires this huge file at the beginning of mining procedures. 2Miners reported the problem to Bitmain’s support desk, which replied with the following, confirming 2Miners’ earlier suspicions:
Sorry for your inconvenience we got the confirm from technical department. E3 miner is a 4G video card. E3 is related to eth algorithm, and DDR capacity is up to the upper limit, so E3 will not be able to continue mining.
To put it simply, the DAG file on ETC reached its upper limits. While ETC mining pools were having problems, Ethereum (ETH) mining pools continued performing as usual. This is normal behavior for Ethash mining. Ethash is the Proof-of-Work (PoW) hashing algorithm used by Ethereum and a variety of other altcoins such as ETC. When low-memory GPU stops mining, it finishes with ETC first, then with ETH since the ETC mining epoch is always ahead of the ETH mining epoch.
The Ethereum Classic mining epoch is currently stands at 328 while it is still 318 for Ethereum. According to the DAG size calculator data, the DAG size for Ethereum accounts for 3.48 GB, while, on the other hand, the DAG size for ETC is at an estimated 3.56 GB at the time of this writing. It will take approximately 40 days for Ethereum to reach 328 epoch putting it in the same unsuitable predicament as Ethereum Classic.