Private Network: Blocktime become over 1 minute when peer number increases

Question

I have a small private ethereum network.

There is only one miner at most. All nodes are connected to miner node and publicly opened another node; always sync. Please note that miner's port is publicly open. You can see an example as follows.

Current Difficulty: 11.73 MH

I do observe that, when network has more than 5 peers or more block time gets larger, which is usually might be over a minute.

For example I observe these block times in a row.

414 seconds, 189 seconds, 363 seconds, 121 seconds, 400 seconds and so on. And even there is in total one submitted transaction. So if I submit multiple transactions and few contract deployment to the network, block time increases over one minutes.

Here is an example of block time most are red.

I have a MacPro, which I used as a miner:

2,5 GHz Intel Core i7
16 GB 1600 MHz DDR3

It used to mine having hash-rate over 4MH/s and now at most 258.4 KH/s after the update on Geth v1.6.2, where I could not find and valid answer related to the issue: Geth 6.2: miner.start() returns null and miner's hash-rate drop for all miners down due to the update .

[Q] What should I do to make my network stable to have block times smaller than 1 minute?

Please note that I can provide and additional information requested. Thank you for your valuable time and help.

Answer 1

including transactions can increase the mining time significantly. You can find some related info to that here .

Long story short, you could lower your gas limit closer to the actually consumed amount, and more important, have more miners on your private net. The logic is really simple: If you have only one computer processing your inputs, it will take longer than if you would split the tasks to a cluster. In the case of ethereum, you would have different miners making the race for a block with always a miner being available to include your transaction.