Creating Your First RAMDisk

Every RAMDisk in Persist is tied to an ordinary folder on your SSD — its backing folder. That folder is where your files rest while the disk is unmounted, and where saved contents are written. Creating a disk comes down to three decisions: which folder, how big, and whether to save on unmount. This page walks through all three, then applies them.

1. Choose a folder

Every disk needs a backing folder, and there are two ways to pick one.

Method 1 — drag & drop. Drag any folder from Finder straight onto the Persist window. That folder becomes the new disk's mount point and backing folder in a single step.

A folder named My RAMDisk being dragged onto the Persist window — Method 1: drop a folder — here “My RAMDisk” — anywhere on the window to turn it into a disk.

Method 2 — the New RAMDisk sheet. Click + Create in the toolbar (top-left). In the sheet that opens, click Choose… next to Mount at and select a folder. You can also give the disk an optional custom name and set its size from the same sheet.

The New RAMDisk sheet with the Choose… button highlighted next to Mount at — Method 2: in the New RAMDisk sheet, click **Choose…** to pick the folder.

Either way, the folder you pick becomes the disk's mount point and its backing folder. While the disk is mounted, that path shows the copy living in RAM; while it is unmounted, the same path shows the real folder on your SSD. Pick an existing folder to have its current contents loaded into RAM on the first mount, or an empty one to start clean. The full model is explained in How it works.

2. Choose a size

Set a size in the sheet's Size field and pick a unit (MB or GB). This number is a ceiling, not a reservation: the disk grows with usage up to the size you set — a 10 GB disk holding 2 GB of files uses roughly 2 GB of RAM, not 10. The sheet spells this out as “Growing up to 10 GB of your system memory”.

The size is not permanent: you can raise or lower it later from the disk's Capacity control. Choosing a ceiling higher than your free RAM is allowed but risky — see Memory & sizing for how much RAM a disk really costs and what happens if it fills.

3. Create the disk

Click Create RAMDisk at the bottom of the sheet. The disk is created and mounted straight away: it appears in the Volumes list on the left with a green “mounted” dot, and its path is instantly usable in Finder and the Terminal.

Select the new disk in that sidebar and its detail view opens on the right — the capacity control from the sheet, plus a whole set of per-disk Options. This is where you tune how the disk behaves; a Discard / Apply pair at the bottom-right commits or drops any change you make. The most important option comes first.

Persist detail view for a newly created disk, showing its capacity, the Memory gauge, and the Normal options list — Selecting the new disk in the sidebar reveals its capacity, the Memory gauge, and the **Normal** options in the detail view.

4. Decide whether to persist changes on unmount

This is the single most important switch in the detail view, because it decides whether your work survives ejecting the disk. RAM is volatile: when a disk is unmounted, everything in it is gone unless it was saved back to the backing folder first.

Persist changes on unmount — on (default): when you eject the disk (or quit the app, or shut down cleanly), Persist copies its contents back to the backing folder on your SSD, so the work is there the next time you mount. Unmounting from Finder or diskutil is handled too — just don't use Force eject.
Persist changes on unmount — off: the disk is pure scratch. Everything written after mount is discarded on unmount. This is what you want for throwaway build caches or temp files where saving would only waste time and SSD writes.

If a disk holds anything you care about, leave “Persist changes on unmount” enabled. Even then, a save only runs at unmount — a power cut or kernel panic while the disk is mounted writes nothing. To narrow that window, keep Periodic background sync on (below), and read Data safety for exactly what survives a crash.

The other Normal options

The remaining switches on the Normal tab are safe to leave at their defaults for a first disk:

Mount at launch — mounts this disk automatically when the app starts. Combine it with Open at Login to have your disks ready every time you log in.
Periodic background sync — keeps an on-disk snapshot refreshed while the disk is mounted (default every 15 minutes), so an unexpected forced unmount loses at most the work since the last snapshot.
Hide from Finder and Volumes — keeps the disk out of /Volumes, the Desktop, and the Finder sidebar. It stays fully accessible at its mount path; this only affects where it shows up. Takes effect on the next mount.

5. Apply your changes

If you touched any option, click Apply (bottom-right) to commit it; Discard throws the edits away. The disk itself is already mounted from step 3, so there is nothing else to do. To take it down later, click the eject icon next to it in the sidebar — which, with persistence enabled, runs the save first.

That's a working RAMDisk. Two pages worth reading next: How it works, which explains why your folder appears empty while mounted, and Data safety, which explains exactly when your data is and isn't written to disk.