System and compressed memory slowing down disk operation

I have win 10 64-bit home on a 4th gen core -i5 laptop. I have a WDC 1T 2.5" USB3 drive. It is about half full. It used to do 60-70MB/s write speed. Since a few days ago, I noticed it has slowed down by a factor of 5-6 to 10-20MB/s. While copying large files, I watched what's going go. The System and compressed memory process was doing a lot of read and write on the disk. If the copy speed reported by the dialog is say 15MB/s, then system compressed memory process is reading 15MB/s and writing 30MB/s. It looks like this process is reading back the content written and writes back. It is consistent over reboot with several large files from 200MB to 7GB in size. A couple of weeks ago I did a file backup. I created a 5GB virtual drive on my SSD and dumped all files to be backed up. Took only 5 minutes to copy the 5GB files to the virtual drive and copy the file to the WDC disk, at around 67MB/s, typical of this type of portable drives. While I was wondering what was going on, I tested the same files with a USB3 dock and a 2TB Seagate drive. Write speed is about 150MB/s. So I thought it was not a problem with all disks. The WDC drive has no compress to save space option, BTW. I wonder what's going on. I have AVG antivirus and I turned it off while copying and same slow 15MB/s speed.

Found solution here:

Windows 10 high Disk usage (100%) I've seen a thread here explaining how to fix it but I seem to have lost it... : techsupport

First reply worked for me. What a royal screw up MSoft?!

Worked for me also thank you.

Oh, that makes sense! I've just turned off lots of notifications I don't need/use. I haven't tested the difference yet but I'm confident this will make a big difference.

Thanks :)