Filesystems and Per-Volume Options

Which filesystem should I pick — tmpfs, APFS, or HFS+?

New disks are always created as tmpfs, and for most uses that's the right answer. The choice lives in the volume's Advanced settings, not the create dialog, precisely because most people should never need it.

Reasons to switch off tmpfs:

• You need Spotlight to index the disk's contents.
• You need a case-sensitive filesystem (some Linux-oriented or cross-platform build setups).
• A tool misbehaves on tmpfs and expects a "real" Apple filesystem.

What actually happens when I change a volume's filesystem?

Filesystems can't be converted in place, so applying a filesystem change to a mounted volume triggers a full cycle automatically: save the contents to disk → recreate the disk with the new filesystem → restore the contents. The content is synced twice, so on a large disk expect it to take a while; the progress bar covers the whole operation and the settings form is locked until it completes. There is no confirmation dialog — clicking Apply is the confirmation.

Changing the filesystem of an unmounted volume is free: the new format simply applies at the next mount.

The save/restore runs even for volumes with Save to Disk turned off — your data survives the reformat either way. The exception: if you shrink the size below the space in use in the same Apply, the erase warning you confirm takes precedence and the disk restarts empty.

Why can't I toggle case sensitivity on its own?

Case sensitivity is baked in when the filesystem is created — it's a property of the format, not a switch. Changing it is a reformat and goes through the same save → recreate → restore cycle described above. tmpfs is always case-insensitive; the toggle only appears for APFS and HFS+.

Why is there no Spotlight option on my volume?

Because the volume is tmpfs, which macOS never indexes — there is nothing to turn on or off. The Disable Spotlight indexing toggle appears only for APFS and HFS+ volumes, where indexing is otherwise on by default.

Corollary: if you need files on your RAMDisk to appear in Spotlight search, tmpfs is the wrong backend — switch to APFS or HFS+.

What do the other Advanced toggles do?

• Hide from Finder sidebar (nobrowse) — on by default. The volume doesn't appear on the Desktop or in Finder's Locations; you reach it through its folder path like any directory. Turn it off if you want the disk to look and behave like a removable drive in Finder.
• Disable FSEvents logging — stops the filesystem-event journal on the volume. Apps that watch folders for changes (build watchers, sync clients) rely on FSEvents; leave this off unless you know you want the disk invisible to such tooling. It can shave overhead on write-heavy scratch volumes.
• Preserve modification times on destination (sync option) — on by default; saved copies keep the files' modification dates. Turning it off makes syncs marginally cheaper but confuses tools that compare timestamps (build systems, backup tools).
• Verify copies by checksum (sync option) — on by default; saves compare content rather than trusting size+date. Turning it off speeds up syncs of huge trees at the cost of weaker change detection — with timestamps also disabled, a same-size in-place edit can be missed by a save. Keep it on for data you care about.

Do Spotlight/FSEvents settings apply immediately?

They're applied after every successful mount and whenever you change the options. These are best-effort niceties: if applying one fails, the mount still succeeds (the failure is logged, not thrown in your face).

Why did my volume's name change when I renamed the folder?

A volume with no custom name displays its folder's name. Give it a custom name in the volume settings if you want a stable label independent of the folder.