For anyone updating your VAIO to Windows 8.1 Update 1, with a computer that experiments 100% Hard Drive activity at OS boot for 10 to 30 minutes or randomly, you may try this:
Type "services.msc" and press ENTER
Find "Sony Digital Media Server", right click it and select "Properties"
Find "Startup Type:", select "Manual".
your computer, if the problem is solved you could also go to "Control
Panel", "Programs and Features" and find the VAIO media server and
If the problem continues you can set
it to "Automatic" again, if you want to. You must keep troubleshooting, Some things that could be affecting the computer are:
Windows Defender (or Windows Security Center)
Some networking issue like a bad/old driver
Windows 8.1 Update 1 seems to use more resources from your computer but hopefully your computer won't be at 100% all time.
After some testing even though the problem has been reduced, the hard drive still shows too much activity, I found out some files were corrupted (this seems to be a common issue with W8.1 U1), the way to test is by running the command
"sfc /scannnow", if the result shows corrupted files with this message "Windows Resource Protection found corrupt files but was unable to fix some of them." then run this command
"Dism /Online /Cleanup-Image /RestoreHealth". You can run "sfc /scannnow" one more time to check the problem has been fixed.
If you indeed have corrupted files, there may be more that sfc is not detecting, one alternative is to test the partition with other software outside of windows like with an Ububtu Live CD and ntfs-3g.
Update: After installing W10 I figured out that most of that activity is normal for this hard drive, the ideal solution would be getting an SSD.