Wednesday, March 10, 2021

The Role of Bootable Duplicates in a Modern Backup Strategy

Adam Engst:

This change increases security even more, but it also prevents all backup apps from creating bootable duplicates because they cannot sign the backed-up System volume. In theory, Apple’s asr (Apple Software Restore) tool makes this possible, but it didn’t work at all until just before Big Sur was released, still has problems, and even now cannot make a bootable duplicate of an M1-based Mac boot drive. On the plus side, Apple has said it plans to fix asr, but who knows when, or how completely, that will happen.


So, even if you can make one, a bootable duplicate won’t help you unless every Mac you want to use it with uses the same chip.


The primary reason for having an up-to-date bootable duplicate is so you can get back to work as quickly as possible should your internal drive fail.


All this is to suggest that the bootable part of a bootable duplicate is no longer as essential for many people as it was when we first started recommending that a comprehensive backup strategy should include one. Since then, it has become far more common for people to have multiple devices on which they could accomplish their work, and much more of that work takes place in the cloud or on a remote server.

The situation with bootable clones is a shame. It was nice to have that option. Even with an SSD, it can take a long time to restore your data to a fresh macOS installation. But it’s likely that, with access to multiple Macs that are mostly in sync, these days I would be more likely to try to resume work on another device while trying to fix the first, rather than boot from a clone of it.

The most important part, as Engst lays out, is to have a multi-part backup strategy. Time Machine is useful, but should not be relied upon. I consider Internet backups and clones to be essential, too, even if they aren’t bootable.


Update (2022-10-06): Howard Oakley:

There are two other good reasons for wanting to build a cloned external bootable volume.

One is to add your own tools to supplement those provided in Recovery Mode, for example a copy of Disk Warrior to enable rebuilding the directory structures of an HFS+ volume, or TechTool Pro for its hardware tests and other tools. Apple has improved those available in Recovery, and the most important third-party disk utilities simply aren’t available for APFS, as Apple still hasn’t provided developers with sufficient information to enable their development.

The other is to provide a fallback macOS known to work, in the event that the upgraded macOS has problems that can’t be solved. These most commonly arose as the result of defective or failed upgrades, which have largely been addressed by Apple’s new updater/installer and the use of the Signed System Volume (SSV), which verifies every last bit in the System volume is correct. There will always be users who want to have a fallback bootable disk, but that can easily be created by a normal macOS install, rather than requiring any form of cloning.

However, without a clone you cannot quickly switch to a fully capable backup system.

4 Comments RSS · Twitter

Bootable backups is a good option to have, but as all other options it should not be the only option or even the main option.
All important and work related files should be stored in git, dropbox or in other cloud solutions anyway. In other words on a server, not on the client machine. Time machine and Backblaze as well as other online services like it is a good compliment too.

But backup strategy with iPads and iPhones is much less robust. I do not want to use unsecured iCloud backup and that and even encrypted iTunes backup is not a complete copy, restoring it does not provide an exact copy of what I have.

It all comes down to Apple's weakness in sync.

Jose Marques

Unfortunately it seems that M1 Macs _require_ the internal drive to boot[1]. So using them as mitigation for a dead or corrupt internal drive likely won't help?


Apple's attempt to provide backup via the cloud is short-sighted.

For a few years following the rise of Facebook, everywhere you looked developers added 'Share with Facebook' buttons to their software. That is on the decline today, because there is more awareness that social media has downsides.

I think we are less than 5 years away from a similar reversal on cloud storage. Because the huge breaches (eg: Equifax, MS Exchange) will not go away, and their impact on regular people, as the leaked data piles up, grows exponentially.

The appeal of storing data 'in the cloud' will not withstand massive, repeated, worldwide hacks of Gmail, iCloud, Amazon, etc. Obviously cloud storage won't vanish, but it won't be a selling point as a back up strategy.

Dmitri: "All important and work related files should be stored in git, dropbox or in other cloud solutions anyway."

Being able to do all my work locally is the whole reason I have a *personal* computer. If I considered "cloud solutions" an acceptable substitute, I wouldn't even have a Mac. I'd put all my data in Google and use a Chromebook.

As Adam says, "The primary reason for having an up-to-date bootable duplicate is so you can get back to work as quickly as possible should your internal drive fail" -- and you want me to park my data on the other side of my *ISP*? I'd like to get back to work sometimes this year!

Also, git isn't a cloud service, and it definitely isn't a backup system. Nobody's adding their ~/Movies/ to a git repo.

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