Quote from: LoyceV on September 16, 2016, 12:22:43 PM

Does anyone know why current blocks take so much longer to download in Bitcoin Core than old blocks? As far I as know the increased difficulty is only related to mining and has nothing to with checking downloaded blocks.

Example: When I start a fresh installation of Bitcoin Core, it starts downloading the blockchain. It quickly goes through the first years with small blocks, then after that it's downloading with more than 2 MB/s continuously. That means at least 2 blocks per second (say 90 seconds to download 1 day's worth of blocks). But when it gets closer to the current date, it slows down.

I'm not sure how you don't know the obvious answer to that question: Because the blocks are larger. Just because the block size limit has been at 1 MB for years, that does not mean that the blocks were actually 1 MB in size. Blocks prior to 2015 and 2016 were usually quite smaller. Note: Downloading these blocks at 2 MB/s isn't the bottleneck, but validating them is. You can speed this up if you add a high "dbcache" setting (e.g. 4-8 GB).

Quote from: LoyceV on September 16, 2016, 12:22:43 PM

Now when I start Bitcoin Core, it downloads fast for a bit, then stops, continues a bit later again, and then downloading stops entirely for a long time. CPU load is low, hard drive I can't hear (and I have no indicator LED). My question is: why is it so slow? Why can't it continue to download 2 MB/s so I can update 3 days in 5 minutes?

It shouldn't stop if it isn't doing anything. Relying on HDD noise is a bad way of testing whether it's actually doing something. If the CPU load is low, then the bottleneck is the IOPS of the HDD.

Quote from: LoyceV on September 16, 2016, 12:22:43 PM

As another test, on my old Atom laptop, it updates 3 weeks blockchain in 2 calendar days. To come back to the statement I quoted: if blocks would be 20 times larger, and I extrapolate this, my old Atom couldn't keep up anymore. And if this gets worse in the future, it could become a limitation for faster hardware too.

Again: Validation time. You could copy over the whole blockchain and do a reindex to check. In other words, reindex builds the blockchain index and chain state from scratch (no downloading). You're going to notice that it takes a lot of time, especially on weak hardware such as yours.

Hint: Something like this should probably be discussed in a separate thread.