Right, on my MacMini htpc (running OS X 10.9.2 Mavericks with the latest updates), I suffered from unbearable slow hard disk performance. Doing some simple measurements showed two huge problems:
- average drive read speed mostly didn't exceed 2 mb/sec
- when loading a lot of files, the whole system got very unresponsive (beach balling all the time) to the point of needing to reboot to restore responsiveness
At first I thought I was dealing with a defective drive, but after reinstalling OS X 10.8 it magically started working properly again. No beach balling, 30mb/sec data transfer speed (still not hyper fast but it is close to the maximum of the simple 2.5 inch drive in the mini). Upgrading to 10.9 once again brought the drive to its knees. Resetting the PMC and NVRAM didn't do anything. Booting in single user mode showed the same abysmal performance. What do??????
Long story short, there's something called the "kext cache" and resetting it solved the problem!!!
To clear the kext caches, type the following in the terminal. You may want to make sure you've backed up your data because I've read some warnings that this could potentially render your system unable to boot (my mini booted fine afterwards thankfully):
sudo kextcache -system-prelinked-kernel sudo kextcache -system-caches
Make sure your start up disk is still selected correctly in preferences, then reboot.
The commands spewed out some warnings on my system, and I had to turn power off and on again to get it out of an endless rebooting attempt. After that though, everything works beautifully now once more!
I have no idea what the commands do exactly, and why they solve the slow hard disk performance, but it solved my problem!
(found this working solution on the MacRumors forums)