There is no maintenance - there is just how the IO subsystem chooses to write new blocks.
* (Sorry to refute the whole premise of your question, but based on the comments - I wanted to reinforce this answer plainly and clearly for everyone.)
An abnormally slow HD is the #1 sign that it's about to fail, so please make a backup before anything else. Put another way, thinking your hard drive is doing extra clean up work actually is the failure mode where it re-maps bad blocks and takes a lot of reads / writes to verify data was saved correctly. It's potentially dealing with reliability and accuracy that has nothing to do with the OS.
To solve the slowness, you'll have to look into the performance or run hardware tests to see why you're not getting the bandwidth or iOPS you expect from your hardware. (as the excellent answer here already details)
Before you do that, I'd probably make a full backup and wipe the Mac and erase / install a clean OS.
You'll know right away if the performance is back or if you have hardware issues. From there, you can restore your accounts and apps and data and then see if it was user level corruption. The work above requires pretty technical skills and lots of time. An erase can happen while you're out for a hike or eating and the testing takes just a short time. If you need to restore from a backup, do that before bed and it usually is done before you wake.