Busy Photo Website - Photos Folder Structure
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I have a busy photo website that has approximately 350,000 photos. The high resolution, downloadable photos are stored in an Amazon S3 Bucket but the thumbnails and previews are stored on my dedicated server.

Currently, I have 350,000 thumbnails in 1 photo folder and the site is growing fast. Am I better off leaving all thumbnails in 1 folder, that could reach a few million, or should I start programatically scaling a folder structure like; photo1, photo2, photo3 and have 100k files in each folder?