I recently noticed that my workstation at work appeared a little slow … well compared to some much older hardware I have anyway. This really manifested itself by horrendously slow performance of the Gnome file manager (Nautilus).
After some digging and examining the the hdparm configuration I noticed that the pre-fetch (-a flag) was set to 256! The manual states that good values for this are 4 and 8.
So I changed the setting to 8 and low and behold responsiveness improved significantly. I’m only speculating, but here are my thoughts on what the problem was.
The manual states that on some newer hard drives pre-fetching is part of the hardware. Now if the OS (or filesystem) is pre-fetching 256 blocks and for each of those the drive itself is also pre-fetching, the hit on the drive should be significant.
I’m not sure if that is really true, but it makes sense to me …