Read/write totally depends on the kind of workload that you are putting on the server.
It vary for too many small files and few large files.
How it writes the data do the disk even depends on the parameters that you set while mounting.
There are by default differences in the ext4 like barrier is enabled write-back, support for larger files etc.
I personally like to read kernel docs, if you might wanna take a look at this: https://www.kernel.org/doc/Documenta...stems/ext4.txt
# iostat -d
this will show you I/O on the partition.
Hope this helps.