I'm experimenting with using btrfs on my Debian Linux armhf system. The rfs is on a micro SD card. On bootup I get the message "Btrfs detected SSD devices, enabling SSD mode". What features does this SSD mode give me exactly?
Traditional hard drives have a spinning disk platter. This means that filesystems can (and do) perform several optimizations. For example, it will locate segments of a file in a contiguous region of the disk, so that when you read different parts of the file, the kernel doesn't have to wait for the platter to spin to a different place. Another optimization done is to locate often-accessed files near each other. Again, this means that statistically, you will spend less time waiting for the disk platter to turn.
By definition, a solid-state drive doesn't have a spinning platter. This means that all of the optimizations done for spinning-platter devices are a dumb idea. All that SSD mode does is turn these optimizations off. Nothing to worry about.