Okay, that makes sense, but something still not right. I started the app again at 9:30 PM, now it's 23:30 PM and still indexing. I have 29 GB of pictures on a class 10 SD card. During the indexing process I measured the disk I/O with a 3rd-party app which gave me 30 to 45 Mb/s read speed. Considering the worst case (30 Mb/s), the whole folder should be processed no longer than 29 * 1024 / 30 / 60 = 16.5 minutes. But Sync could not finish with it during 2 hours. Am I missing something?