My late-2013 Macbook Pro 13" has been increasingly laggy and slow for the last several months. Replacing the SSD helped a little, but now it is beach-balling even opening a single new tab. Overall CPU usage is low (mostly WindowServer) but I was alarmed to see the amount of disk writes that kernel_task is doing (about 20GB per day).
Checking with smartctl then showed that over the 4 months since I replaced the SSD, it has done over 70TB of writes! I have no idea what it could be writing. My usual apps are Google Chrome, Terminal, Preview (for pdfs) and TeXshop and background apps (Dropbox, Google Drive, etc). How can I figure out what is lagging everything/causing kernel_task to do so many writes?
Best Answer
It's probably Dropbox or Google Drive. I've seen similar problems. Typically it's caused by Dropbox or Google Drive repeatedly downloading the same files over-and-over. They are both somewhat buggy programs.
Do you have any symbolic links in either your Dropbox or Google Drive? Neither deal well with symlinks; Dropbox specifically does not support them. (See https://www.dropboxforum.com/t5/Files-folders/Symbolic-link-on-Mac/td-p/27496 and https://help.dropbox.com/installs-integrations/sync-uploads/symlinks).
You can find symbolic links from the Terminal with this command:
or to see where it points:
You can also run a program that monitors all writes to your hard drive by file, to diagnose the problem youself. Turn off System Integrity Protection and run opensnoop or iofileb.d.