Bitcoin core initially downloads IBD quite fast , then it slows down a lot , What could be the reason? [duplicate]

Question

I am trying to setup a bitcoin node , ran bitcoin core and it started the download process quite fast ETA 18 hours , gradually the speed decreases . When I started download it showed like 17 hours ETA, and this continued for around 2-3 hours. **

Progress Increase Per Hour : 5.5 % 
Estimated time left until synced : 17 hours

**

after 2 - 3 hours , the progress starts going down .

After 5 hours

**

Progress Increase Per Hour : 0.71 % 
Estimated time left until synced : 5 days

**

I have enough empty hard disk around 200 GB free, RAM is also 4 GB .

I stopped the download , renamed the Bitcoin download folder and started download again fresh.

Same issue happened , initially the speed remains high but gradually after around 40 GB of download it starts going down drastically .

My configuration are

Prune block storage to : 2 GB
Size of database cache : 2048 MB
Number of script verification threads : 0 

Is there a bug in bitcoin-core or is it an expected behavior ? What can I do to speed it up ?

Answer 1

Progress Increase Per Hour : 5.5 % Estimated time left until synced : 17 hours

This estimate is based on samples: src/qt/modaloverlay.cpp#L107

It will keep changing and some blocks will be synced faster compared to others.

Is there a bug in bitcoin-core or is it an expected behavior ?

Doesn't look like a bug. Maybe estimate logic can be improved or users can look at the number of blocks left to be synced.

What can I do to speed it up ?

• Increase RAM and dbcache
• Increase number of threads or CPU/cores that are used for script verification