A friend/customer of mine, Rich, was having problems with his Lightroom. It was as fast as molasses on a cold day.

I tried to help him over the phone, no luck. Time for TeamViewer. It’s some software so I can log onto his computer without having me to drive there.

Yes, it was slow, it was very slow. A quick looking around, nothing too obvious. Switching to the Grid View was extremely slow. I started the task manager to see what was happening and I saw a very high IO, it’s the one in red. IO is Input/Output. It’s usually related to disk IO, but it could be USB IO

Slow Lightroom: Disk IO

Slow Lightroom: Disk IO

The question was what’s causing the heavy disk IO? I asked Rich if he knew. Nothing changed, no new install. It was be getting slow for the “last while” with no idea for how long was the last while. I started looking around, checking the Lightroom catalog… No, it was working fine…

I kept on looking, then suddenly the “stroke of genius” (always ggood to send oneself compliments). The problem was the antivirus. The antivirus has real-time protection. Meaning that the antivirus checks for every disk write and Lightroom does a lot of disk reads and writes. Every time Lightroom builds a preview, it saves it to the preview directory. Every time you switch to the Develop module, the 1:1 preview is built (if it doesn’t exist yet), saved and displayed.

Rich was using the Microsoft Security Essentials, but it’s the same for all the other antiviruses.


  • Excluded files and location: I excluded the directories of the Camera Raw Cache settings (from the preferences|file handling) and of the catalog (from the catalog settings|location) .

And we were almost zooming again. I got him to run the Windows Disk Defrag 4 times to reorganize the disk.

Why 4 times? Running it once is not enough, because the Disk Defrag creates spaces/holes where other files can move, especially with the previews and with the raw cache.