Copy Shelter and Arq, compared

Short answer: Arq is the closest thing to this app that exists, and if you already use it and are happy, there is no argument here that should move you.

The differences are narrower than a marketing page would like: how many storage backends, how the verification is framed, and how much the software asks you to understand before it will help.

Why this page is the honest one

Most comparison pages on vendor sites pick a competitor that loses. This one does not. Arq has been doing the same fundamental thing for well over a decade: encrypt on your machine, write to storage you choose, keep versions, and do not hold your data hostage.

Several claims on this site's front page are not unique against Arq, and it would be dishonest to imply otherwise. Arq verifies backups on a schedule. Arq publishes an open source restore tool. Arq lets you restore without a paid license. If you are comparing us on those three, we are level.

Where Arq is the better answer

You want the widest choice of storage. Arq speaks to a long list of cloud providers directly, SFTP among them. Copy Shelter writes to a drive, a network share or a cloud sync folder, to S3 compatible storage such as Amazon S3, Backblaze B2, Cloudflare R2 and Wasabi, to a WebDAV server, and to another Mac you own. If your storage is on Arq's list and not on that one, Arq is the answer.
You are on Windows as well. Arq runs on both. Copy Shelter is a Mac app today.
You have been running it for years. An archive with real history in it is worth more than a feature comparison. Do not throw away a working multi-year backup to try something newer; run the new one alongside if you are curious.
You want very fine control. Arq exposes a lot of knobs. Some people want that.

Where the two differ

What the interface leads with. Copy Shelter's main screen is a statement about where you stand: what is protected, which copies exist, when each was last verified, and a score out of 100 that counts only what has been checked. It is designed to be readable by somebody who does not want to learn a backup tool. Arq's is designed around configuring backup plans.
Verification on by default. Both verify. In Copy Shelter a copy that has not been read back is not counted as a copy anywhere in the interface, which is a different thing from having verification switched on.
The failure vocabulary. Copy Shelter is built to name what is missing: this destination has not been seen since this date, this piece no longer matches its hash. That is a design goal, and it is the thing we would most want compared.
The free tier. Copy Shelter is free for one backup location, with no trial to run out, and that free tier includes the full restore and the verification pass. Check Arq's current pricing on their own site. We are a competitor.

What both of us do that Time Machine does not

Worth stating, because for most people the real comparison is against what is already on the Mac:

Write to a folder. No disk has to be formatted for the purpose.
Encrypt with a key you hold, before anything leaves the machine. The destination has no say in it.
Use storage you already pay for, including a cloud folder, which Time Machine cannot use at all.
Verify on a schedule, which Time Machine does for network destinations occasionally and for local disks not at all.

The full Time Machine comparison is here, including the rows where Time Machine wins.

Running both

Nothing stops you, and for an archive that matters it is a reasonable thing to do. Two tools writing to two destinations fail for different reasons, which is most of what the 3-2-1 rule is really asking for. Point them at different disks.

The thing to check about any of us

Whichever you pick, ask the same question before you rely on it: can you get a file back today, from the backup as it exists now, without the vendor. Not in principle, actually. Restore one file this afternoon and see.

Copy Shelter's answer is a documented format and csctl, a free single file tool that reads a backup with nothing but the folder and your passphrase. Arq's answer is its own open source restore tool and a restore-only mode. Both are real answers, and a tool without one is the thing to be suspicious of.

Common questions

Is Copy Shelter an Arq alternative?

It is aimed at the same idea, yes: encrypt on your machine, write to storage you control, keep versions, and do not depend on the vendor to get your files back. It is a newer and simpler tool with fewer storage backends and a stronger opinion about telling you when something is wrong.

Can I move an Arq backup into Copy Shelter?

No, and nor the other way round. The repository formats are different. The migration path is to start a new backup and keep the old archive until you are satisfied the new one restores, which is the right way to move between any two backup tools.

Does Copy Shelter support S3 or Backblaze B2?

Yes. The backup itself, or a second copy of it, can go to Amazon S3, Backblaze B2, Cloudflare R2, Wasabi or any other S3 compatible storage, or to a WebDAV server such as Nextcloud. It also writes to any folder the Mac can reach, including external drives, network shares and the sync folders of iCloud Drive, Dropbox, Proton Drive and Google Drive.

Which is better for a non-technical person?

We would say ours, and we are not a neutral party. The honest version: Copy Shelter is built so the main screen answers where you stand without configuration, and Arq is built to be configured. Try both, they both let you restore before paying.

Why publish a page that says a competitor is good?

Because you will find Arq anyway, and a comparison that pretends otherwise tells you more about the company than about the software. If the honest comparison loses us a sale to somebody Arq suits better, that is the correct outcome.