Sony VAIO 100% hard drive activity.

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:

Press WIN+R

Type "services.msc" and press ENTER

Find "Sony Digital Media Server", right click it and select "Properties"

Find "Startup Type:", select "Manual".

Restart your computer, if the problem is solved you could also go to "Control Panel", "Programs and Features" and find the VAIO media server and uninstall it.

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:

Readyboost

Indexing

Pagefile

Defragmenter

Antivirus Scan

Windows Defender (or Windows Security Center)

Windows update

Superfetch

Raid driver

Some networking issue like a bad/old driver

Corrupted files

Windows 8.1 Update 1 seems to use more resources from your computer but hopefully your computer won't be at 100% all time.

Update:

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 Window 10 I figured out that most of that activity is normal for this hard drive (It's probably Windows 10 fault, once you start needing more RAM, virtual memory kicks in and this is the first symptom), the ideal solution would be getting more RAM and possibly a Solid State Drive.