Catalog a folder or drive. On the Catalog page, click Catalog a Folder… and pick a folder or a whole drive. Review the HD preview settings in the confirmation panel (size, quality, and the estimated disk space), then click Start Cataloging. It runs in the background, and re-running the same folder later is quick because photos already cataloged are skipped.

HD previews. Each cataloged photo gets a small thumbnail (fixed at 512px) and an HD preview at your chosen size and quality (default 2048px, q80). The HD preview is what you see when the drive is offline, and what syncs to a paired phone. Bigger previews look sharper zoomed in but use more disk, and the confirmation panel shows the estimate before anything runs. New previews always use the current setting; existing ones keep the setting they were made with until you rebuild them with Preview Quality… ▸ Regenerate Previews.

Re-index, Remove, Forget. Re-index re-scans a folder for new or changed files. Remove takes one folder out of the catalog, and Forget drops a whole drive. Both delete catalog entries and cached previews only. The files on your drives are never touched, and re-cataloging brings it all back.

Deleted or moved photos. Re-indexing also forgets photos that have left the drive, so files you deleted, and folders you moved or reorganized, stop showing in the catalog — which is also what keeps photo counts honest after a reshuffle. Find missing files on a drive does the same thing without a full re-index: it counts what is gone, shows you the number, and waits for you to confirm. A photo you also cataloged on another drive keeps that copy and stays. Both need the drive connected, and neither will touch a drive that is unplugged or whose identity no longer matches — an unplugged drive is never read as a drive full of deleted photos. A photo is forgotten only when the drive answers that the file is not there; a permission problem, a read error, or a share that is asleep leaves the entry alone.

Storage & Backup. The catalog has two parts: the database (photo records, metadata, saved searches, settings) and the preview store (cached thumbnails and HD previews, usually the bigger of the two). You can move the preview store to another drive when it outgrows this computer, back up a timestamped snapshot of the database, and restore from a backup on the next launch. Two tips: take a fresh backup after moving the preview store, and back up to a different physical drive than the one the catalog lives on.