The default one is 128k. What is the impact of reducing the block size below to 128K e.g. 64K, 32K,16K?
We do not enforce a minimum but do not recommend going below 128KB. That said, I am only sure we would not function if you were to drop below 128 Bytes since that is our minimum record size on disk.
The configuration we ship normally has write-block-size set to 128 KB but the actual default, if parameter were left out of the config, is 1 MB.
The write-block-size also determines the maximum record size so lowering one lowers the other.
By varying block sizes with the dd command I can observe that the performance of my local SSD drops if I go below 128 KB. The highest performance I see is by using 128 KB but 256 KB is nearly the same. There is a noticeable, but not terrible, drop when using 512 or 1024 KB with 1024 performing a bit better than 512.
Many users have a use case where they keep appending to records, so allowing larger records may, may in this case, also increase the amount of bandwidth being used for reads and writes.