Intermittent horrible SD card write performance

I am using Colibri T30 V1.1E module with Windows CE 7 V1.4 image. I created a native C++ app to fill a file on the SD card with 240 MB of data with 1 MB chunks. Each time I run the test I use a different filename.

Normally each pass takes approx 22 seconds to complete. I’ve seen as fast as 21 seconds and as slow as 27 seconds.

After about 8 to 10 times (so 8 to 10 files exist of 240 MB each) the test will take over 2 minutes to complete. The card is not getting full when this happens, its about 30% full with 8-10 files. The next test seems to run at normal speed.

I am using Patriot brand class 10 8 GB microSD card formatted at FAT32.

Any suggestions?

@ed.nafziger: Are you able to reproduce the same issue with any card (other brand)? If not, I assume this related to any background task on the card. If it is reproducable with any card, let us know, so we can check it closer on our side.