A folder, not a copy

Last verified 4 September 2026. The first half of this page is about a way of working with storage; the second half is about the apps that offer it, PolyDrive among them. Where it says what another product does, the claim links to that product's own page, so you can check it and so you can tell when this page has gone stale. The comparison table is the companion to this page: that one is the facts in rows, this one is the reasoning.

You already use a mount

Open Finder and look at iCloud Drive. Some files carry a small cloud with an arrow. Apple's own description of that icon is the whole idea in two sentences: the file “is only in iCloud. You must be connected to the internet to work with the item, unless you download it to your Mac.”1 The file is listed, it has a name and a size and a date, you can double-click it — and it does not occupy your disk until you do. That is a mount. Apple never called it one, and you have been using it for years.

The other way to have cloud files on a Mac is the way Dropbox made famous: a folder that is kept identical to the cloud by copying everything, in both directions, all the time. That is sync. The two look alike in Finder and behave nothing alike, and the cleanest way to see the difference is one you already understand.

Streaming, not a record collection

Sync is the record collection. Every album you own is on the shelf, on every shelf you own, and a new shelf spends its first afternoon being filled. A mount is the streaming service. The catalogue is all there and nothing plays until you press it; what you have listened to lately is cached, and there is a “download” button for the flight. The analogy is unusually exact, because the awkward parts line up too:

That last row is the honest cost, and the streaming service has the honest answer to it: a download button. On iCloud Drive it is “Keep Downloaded”.1 On a PolyDrive drive it is “Keep Available Offline” in the right-click menu, and a pin badge in Finder shows what is being kept. Choose a folder and everything inside it comes along.

A mount does not mean nothing touches your disk. It means your disk holds what you use, in the amount you use it, and a file arrives in pieces rather than whole. Open a 1.35 GB video from inside VLC or IINA and play ten seconds from anywhere in it, and about 20 MB lands — the pieces holding those ten seconds, and nothing else.3 The pieces stay cached, and the space can be handed back from the same menu.

When sync is the right answer

If the whole of your work fits in one folder, that folder fits comfortably on your disk, and you are often somewhere without a connection, sync is better, and the provider's own free app is the best sync client for that provider. PolyDrive mounts Dropbox, Google Drive and OneDrive too, but if one of those is the only place your files live, you do not need it.

A mount earns its place when the storage is bigger than the machine, or when it is scattered: a bucket here, a Seafile library there, a NAS on the desk, a phone on a cable, a Linux SD card in the reader. Six places, six apps and six menu-bar icons competing for your disk, or one Finder sidebar. That is the case PolyDrive is built for.

So which mount, then

PolyDrive is not the only app that does this. Mountain Duck, ExpanDrive and CloudMounter all mount storage into Finder, all fetch contents on demand rather than syncing everything to disk, and all connect straight to your provider with no server of their own in between. On the thing this page has spent its first half explaining, the four of us agree, and we are all reasonably good at it.

One difference is worth knowing before you read anyone's feature table, because it is about which half of this page a product comes from. Mountain Duck grew out of Cyberduck, a file-transfer client, and it still arrives set to synchronise: its own documentation explains how to “disable synchronization by default for all bookmarks by switching to Online”, and describes its Smart Synchronization mode as files “copied to a local cache… prior synchronization with the server”.13 Mounting without syncing is its Integrated mode, which arrived in version 5 in August 2025. PolyDrive only ever mounts. That is not a complaint about a good product — it is the difference between an app that learned to mount and an app that does nothing else.

The rest of the differences are facts in rows rather than reasoning, so they live on the comparison table: how many storage services each one opens, what each installs on your Mac, and how much a seek into a large video actually downloads. Two of those rows are the ones we would point at first, because they are not on any of the other three lists at all — an Android phone on a USB cable, and an ext4 disk out of a Raspberry Pi, both of them just folders in Finder.

Whose format are your files in?

One question, though, belongs here rather than in a table, because the answer is a view of the world and not a feature. Two of the apps on this page will encrypt what you store, so that the provider holds only ciphertext. What is worth asking is not “does it encrypt” but “who else can open the result”, because encryption is the one feature that can turn your files into hostages of the app that made them.

CloudMounter's encryption is its own. Its description is that you “encrypt data before sending it to the cloud and make it accessible only from your own CloudMounter app”;5 the algorithm is AES-256, and we could find no published description of the format or of any other application that opens it. That is a legitimate design, and it means the day you stop using CloudMounter is the day you decrypt everything first.

PolyDrive uses Cryptomator's vault format instead of inventing one. Cryptomator is open source, its architecture is published down to the primitives — scrypt for the key, AES-SIV for names, AES-GCM or AES-CTR for content — and its cryptography was independently audited by Cure53 in 2017.6 It has its own apps for Windows, macOS, Linux, iOS and Android, and Mountain Duck opens the same vaults.7 A vault PolyDrive writes is a vault three other vendors' software can read. If PolyDrive vanished tomorrow, your encrypted files would not notice. We think that is the only honest way to sell encryption, and we accepted the cost: PolyDrive opens vaults that already exist rather than creating new ones, so you make the vault in Cryptomator first.

Format is not only the bytes. Often a file's name carries nothing — a camera or a scanner numbered it — and everything that identifies it lives in the path above, in folders someone took the trouble to name. A service built on a flat library asks you to give that up at the door: the files arrive, the tree does not, and what the folders said about them is gone at the one moment you can no longer reconstruct it. That is a fair trade for what such a service gives back, and it is still a trade. A mount does not make it, because nothing is imported — the folders on the storage are the folders in Finder, under the names whoever made them chose.

The same question applies to something less visible than your files: your credentials. PolyDrive keeps them in the macOS Keychain and has no server to put them on. ExpanDrive's security page says its versions “2025 and earlier do not store your credentials … in the Cloud” and that with the web client it plans for 2026, “we will begin to store your credentials in the Cloud”.8 That is a stated intention, not a shipped change, and they promise clear notice. It is still a different answer to the question.

What we are not claiming

• That a mount is always better. See above. If your life is one Dropbox folder, use Dropbox.
• That PolyDrive gives you a real volume. A File Provider mount is a folder under ~/Library/CloudStorage, not a disk in /Volumes. If you need the latter — because a tool insists on it, or because you want a path outside a protected location — CloudMounter's macFUSE mode is the one that gives it to you, and it is the reason that mode exists.4
• That a video plays the instant you double-click it. Fetching a file in pieces only helps when the program opens the file itself — VLC's or IINA's own File › Open, a script, the command line. Double-click it in Finder and macOS downloads the whole thing first, exactly as it does for iCloud Drive, and no app built on this API can opt out of that.
• That we have the most controls. CloudMounter gives each drive a refresh interval you can set from 20 seconds to 30 minutes, a lifetime after which cached files are deleted, and on macOS 15 a choice of which volume the cache sits on.12 PolyDrive has none of those. A folder is re-read when you open it and its listing is over a minute old, “Refresh from Server” re-reads on demand, and space is handed back with “Stop Keeping Offline” or “Remove All Local Copies”. No timer to set, no size cap to set. If you want those knobs, CloudMounter has them and we do not, yet.
• That we are the only path for scripts or AI agents. Every File Provider app gives a script an ordinary directory. What differs is which storage is one click from being that directory.
• That we cover the most services, or run on the most systems. rclone reaches more backends than anyone, free, from a terminal — and where it reaches one we do not, you can put it behind a local bridge and keep the Finder half of this page's argument. ExpanDrive is free for personal use and runs on Windows and Linux; CloudMounter has a Windows edition;9 Mountain Duck has SharePoint and enterprise deployment tooling. PolyDrive is a paid app for the Mac, and only the Mac.

What we are claiming

Four things, each of them checkable rather than a matter of tone.

• Your files stay yours. Encryption in an open, audited, multi-vendor format; credentials in your Keychain and nowhere else; no PolyDrive account, because there is no PolyDrive server for one to live on.
• What the app did is written down, on your Mac. An activity log of drives connecting, folders refreshing, transfers finishing and uploads that failed — named, with the reason the service gave. Local, exportable, and the first thing to look at when something did not arrive.
• Every version says what changed. The release notes are on the App Store listing, version by version.10 When the problem turns out to be a provider's, we say that too: in September 2026 we wrote up three defects in one provider's API, sent them over, and re-tested the day they reported a fix.
• You buy it once. One purchase on the Mac App Store, updates included, no subscription to cancel later — less a price than a promise about the relationship, since a mount app sits between you and your files every day. Mountain Duck's App Store edition, for comparison, is sold as a subscription.11

Sources

1. Apple, “Check your iCloud Drive file and folder status on Mac”: the In iCloud status “indicates that the folder or file is only in iCloud. You must be connected to the internet to work with the item, unless you download it to your Mac”; the Keep Downloaded status “indicates that the folder or file is kept downloaded on your Mac, even if it's an older item and more storage space is needed”. Read 4 September 2026. support.apple.com
2. Dropbox, “What's a conflicted copy?”: “A conflicted copy is a file that Dropbox creates when multiple people edit the same file at the same time”, listing among its causes that “someone edits a file offline while someone else edits the same file” and that “a file is left open on another user's computer, which Dropbox saves as a new edit”. Read 4 September 2026. help.dropbox.com
3. Measured 7 September 2026 on macOS 26.5.2 with a Cloudflare R2 drive: a 1 351 001 061-byte, 13.5 Mbps 1080p video. VLC playing ten seconds from 400 s made eleven ranged fetches and left 20 MB on disk; the same at 780 s did the same. After three command-line reads, twelve seconds in IINA and two ten-second stretches in VLC, 61.7 MB of the file's 1288 MB had been downloaded. Times and amounts depend on your connection and on how far the storage is from you.
4. CloudMounter, “Types of drive mounting used in CloudMounter”: a “macOS Native Drive”, “a native way to mount cloud storage on macOS” available “since macOS 11.3” with “support for working with files offline”; a “macFuse Drive”, which “is not available in the version of CloudMounter distributed through the App Store”; and a “Network Drive”, of which “when using this type of drive mounting and performing a large number of simultaneous file operations, the list of files may take a long time to load or the disks may be disconnected”. The page does not name File Provider; 11.3 is the release that made it usable on macOS, and the native mode's offline behaviour and its cache-volume option are File Provider features, so we treat it as such. Read 4 September 2026. cloudmounter.net
5. CloudMounter, “Strong cloud encryption software”: “Encrypt data before sending it to the cloud and make it accessible only from your own CloudMounter app”, and “AES-256 encryption uses a symmetric-key cryptographic algorithm”. Its FAQ on using encryption lists the mode's limitations, among them that “Google Docs are skipped during Google Drive encryption”. Neither page describes the on-disk format or names another application that can open it. Read 4 September 2026. cloudmounter.net/cloud-encryption, cloudmounter.net/faq
6. Cryptomator's published security architecture specifies the vault format: a masterkey protected with scrypt and AES Key Wrap, filenames encrypted with AES-SIV, and file contents in either the SIV_GCM or SIV_CTRMAC scheme. The 2017 cryptographic audit by Cure53 is published in full. The project's home page: “No backdoors, no expiration date thanks to open source.” Read 4 September 2026. docs.cryptomator.org, cryptomator.org/audits, cryptomator.org
7. Mountain Duck documentation, “Cryptomator”: “Mountain Duck includes support to create and access Cryptomator interoperable vaults.” Read 4 September 2026. docs.mountainduck.io
8. ExpanDrive's security page: “ExpanDrive versions 2025 and earlier do not store your credentials (passwords, keys, and authentication tokens) in the Cloud… We are working on a Web-based client for ExpanDrive that we intend to release in 2026. When we do, we will begin to store your credentials in the Cloud. We will provide clear notice when this transition occurs.” Read 3 September 2026. docs.expandrive.com/security
9. CloudMounter's home page lists Dropbox, OneDrive, Amazon S3, Google Drive, WebDAV, SFTP and FTP for both platforms, with pCloud, Box, Backblaze, MEGA and OpenStack added on macOS, and offers a Windows edition. Read 4 September 2026. cloudmounter.net
10. PolyDrive's Mac App Store listing carries the release notes for every version under Version History. apps.apple.com
11. Mountain Duck's Mac App Store listing: users “are eligible to run version 5 with no limitations for up to one year after their purchase date before they are required to purchase a monthly or yearly subscription”. Read 4 September 2026. Its direct-download edition is licensed differently; check mountainduck.io for that. apps.apple.com
12. CloudMounter's per-drive menu, in the current Mac App Store build on 4 September 2026, offers “Content refresh interval” with 20, 30 and 45 seconds and 1, 2, 5, 10 and 30 minutes, 1 minute selected by default, next to “Change cache volume”. Its documentation, “Optimize CloudMounter cache settings on your Mac”, adds: “Cached files lifetime — cached files are automatically deleted when the time set in this option runs out”; “Change cache volume lets you choose where CloudMounter stores cached data for your mounted cloud drives”, “available when using the macOS Native Drive type of mounting drive and on macOS 15 or later”, APFS (Encrypted) volumes only. Read 4 September 2026. cloudmounter.net/faq
13. Mountain Duck's documentation, under Preferences › Synchronization: “Change the default synchronization option. You can disable synchronization by default for all bookmarks by switching to Online”; and of Smart Synchronization, that files are “copied to a local cache… prior synchronization with the server”. Its Integrated connect mode, the one that mounts through the operating system's own API as PolyDrive does, was introduced in Mountain Duck 5 on 19 August 2025. Read 7 September 2026. docs.mountainduck.io, mountainduck.io/changelog

Mountain Duck, ExpanDrive, CloudMounter, Cryptomator, Dropbox and iCloud are trademarks of their respective owners. PolyDrive is not affiliated with, endorsed by, or sponsored by any of them. The statements above reflect each vendor's own published information on the date at the top of this page and may have changed since. Found something out of date or wrong? Email [email protected] and we will correct it.

A one-time purchase, no subscription. macOS 15.4 or later.