Anything-sync-daemon (asd) is a is a diminutive pseudo-daemon designed to manage target directories in tmpfs and to periodically sync them back to your physical disc (HDD/SSD). This is accomplished via a symlinking step and an innovative use of rsync to maintain back-up and synchronization between the two. One of the major design goals of asd is a completely transparent user experience.
https://wiki.archlinux.org/index.php/Anything-sync-daemon#Edit_.2Fetc.2Fasd.conf
解决SD卡频繁读写问题 Anything-sync-daemon 映射linux目录到tmpfs并定时同步
原文：http://www.cnblogs.com/geektown/p/5004556.html