A macOS build machine shows mds_stores consuming CPU and hammering the disk whenever a build runs. What is that process doing, and how do you control it for specific volumes or directories?

## What the processes are Spotlight is a metadata index, not a filename index. `mds` is the server; `mds_stores` maintains the index stores; `mdworker` and `mdworker_shared` are short-lived workers that run **importer plugins** to extract metadata from individual files — text content, EXIF data, document properties, and so on, depending on the file type. The indexer is driven by filesystem change notifications: when files appear, change or disappear, work is queued. On a laptop that is invisible. On a build machine that writes and deletes tens of thousands of intermediate objects per run, it means a second workload racing the build for CPU and disk, and an index that is stale the moment it is written. This is the classic "why is my CI Mac slow" answer after the build itself. ## Controlling it per volume `mdutil` is the management tool for indexing state: ```bash mdutil -s /Volumes/Build # status: indexing enabled or disabled sudo mdutil -i off /Volumes/Build # stop indexing this volume sudo mdutil -i on /Volumes/Build # resume indexing sudo mdutil -E /Volumes/Build # erase the index and rebuild it mdutil -a -s # status for all volumes ``` The distinction that matters is `-i off` versus `-E`. Turning indexing off stops the work. Erasing the index throws away the store and starts a **full reindex**, which is the heaviest thing you can ask Spotlight to do. `-E` is the right move for a genuinely corrupt index producing wrong search results; it is the wrong move for high load, where it makes the symptom worse for the next hour. Also note that the boot volume is not an ordinary target. macOS protects system content, and Apple's supported ways to exclude content there are the privacy list and per-directory markers rather than switching the system volume's indexing off wholesale. ## Controlling it per directory Two file-level markers do the job without disabling a whole volume: - **`.noindex` suffix on a directory** — name the directory `artifacts.noindex` and its contents are skipped. This is the surgical option for a build output tree, and it survives being recreated by the build if the build creates it with that name. - **`.metadata_never_index`** — an empty file at the **root of a volume** tells Spotlight not to index that volume. It is a volume-level marker, not a per-folder one; dropping it inside a subdirectory does nothing, which is a common misunderstanding. The graphical equivalent is the Spotlight privacy list in system settings, which is what you use for a path you cannot rename. On a managed fleet the same exclusions can be delivered centrally as policy rather than configured per machine. ## The cost of excluding An excluded path is invisible to Spotlight, and therefore to `mdfind` — the command-line query interface — and to anything built on the metadata index. `mdls` shows the attributes Spotlight has recorded for a file, and on an excluded path it will show essentially nothing. On a build machine nobody cares; on a shared workstation, silently excluding a user's project directory turns into a support ticket about search being broken. Say the trade-off out loud when you propose the exclusion. ## A related trap: network and external volumes Spotlight also indexes mounted external and network volumes when enabled, which is how a NAS mount ends up generating sustained traffic and CPU on a machine nobody is searching from. `mdutil -s` on the mount point tells you whether that is happening, and the same `-i off` or `.metadata_never_index` at the volume root stops it. ## The shape of a good answer Name the processes and say what they are actually doing — importer plugins over change notifications, not a filename scan. Separate the volume-level control (`mdutil -i off`) from the directory-level markers (`.noindex`, the privacy list) and from the destructive rebuild (`-E`) that people reach for by mistake. Close on the trade-off: everything you exclude leaves the searchable index.