What about disk I/O? Disk I/O is usually a major bottleneck because Bitcoin Core constantly reads and writes from storage. The updating of the UTXO set during validation causes a lot of disk I/O and it can often end up being the bottleneck.
If you increase the dbcache parameter, more of the database can be held in memory which improves the sync time.
On a SSD, but will increase.
How do you know?
https://bitnodes.io/dashboard/?days=730Did you measure that or is that what the estimate says?
Based on the estimate and how much I've managed to sync over the last three days.
More importantly when I added a bunch of Nodes manually the estimate dropped to 40 hours. and speed of sync dropped dramatically.