Just looking through activity monitor and noticed that apart from kernel_task, it is consistently the second process in terms of amount of data wrote to disk. I only ask as I had a disk writes diagnostic report generated for what I think is the first time. Today, it's wrote have a GB of data, the only one overtaking it is kernel_task which wrote 3GB. Is that amount normal/ the fact it's second normal?
Which processes are top 1, 2, 3, and so on, on the list of processes writing most to the disk will and should change depending on your particular use of the computer. There's no "normal" list in that sense.
If you're asking just because you've looked at Activity Monitor and thought "is this normal" - then yes, it is normal, and you shouldn't worry.
If you're asking because you have a specific problem with your computer, I would recommend asking advice for that problem instead of focusing on
diskmanagementd as a potential cause.