Your NAS Is Loud Because of Docker and Syncthing (and How to Fix It)

You buy a NAS for silent, always-on storage. It sits in a corner, humming quietly, doing its thing. Then you install Docker. Then Syncthing. Then a few containers. Suddenly the HDDs never stop. Seeking, spinning, clicking. Not occasionally - constantly. At 2am you can hear it from the next room. This is what happened, why it happens, and how to make it stop. What's Actually Causing the Noise Mechanical HDDs make noise when the read/write head moves. The more random the I/O - small reads and writes scattered across the disk - the more seeking, the more noise. Sequential writes to a single file are quiet. Random I/O across thousands of small files is loud. Docker and Syncthing are both pathological for HDDs in different ways. Docker overlay2 Docker's default storage driver is overlay2. Every container runs on top of layered filesystems - the image layers are stacked, and a thin writable layer sits on top for each running container. Every file operation inside a container that touches a file from a lower layer triggers a copy-on-write : the entire file gets copied up to the writable layer before the write happens. On an SSD this is fast and silent. On spinning HDDs with mechanical heads, every copy-on-write is a seek, a read, and a write - often scattered across the disk. And it's not just copy-on-write. Docker's overlay2 metadata lives in small files across a deep directory tree. Container startup reads dozens of these. Log rotation writes to them. Health checks touch them. Any container doing anything at all generates constant scattered I/O. Syncthing's 60-Second Heartbeat Syncthing uses BoltDB as its internal database - it stores file indexes, sync state, and peer information there. BoltDB flushes to disk every 60 seconds regardless of whether anything changed. On a busy sync folder with thousands of files, this flush isn't a single sequential write. It rewrites pages across the B-tree structure, which means multiple seeks across the database file. Quiet when it's a