Understand Joe’s Basic Backup Strategy

Since I started writing about Mac backups in 2004, the basic strategy I’ve followed and recommended has consisted of three main components. Now, for the first time, I’m altering my practices and recommendations. There are still three components, but one of them is now optional, and carried out differently than before:

• Versioned backups: Use Time Machine or another backup app to store versioned backups—multiple copies of each file, so you have both the latest version and numerous previous versions. Update your versioned backups incrementally (copying only new or changed data each time) at least daily, and preferably more often.

• Bootable duplicate: Optionally, depending on your circumstances, create a bootable duplicate of your startup volume on an external SSD or hard drive, and update it regularly. (I explain my new reasoning in Why Create Bootable Duplicates (or Not)?.) If you choose not to create a bootable duplicate, you might want to add something else in its place or make other alterations to your strategy; see Alternatives to Bootable Duplicates.

• Offsite copies: Keep at least one backup copy of your important data somewhere safely away from your Mac—in another building, at least, and perhaps even in another part of the world (in the latter case, by using a cloud backup service).

In some cases, you might be able to use a single backup drive for both versioned backups and a bootable duplicate—for example, by dividing it into two partitions (see Why Use Multiple Partitions (or Not)?) or by using backup software that creates a versioned bootable duplicate (see Bootable Duplicates with Versioning). Otherwise, you’ll want a separate drive for each type of backup, though even if you use a combined drive, you might choose to add a second drive for extra peace of mind. I also discuss using online storage for versioned backups, which counts as an offsite copy and could reduce the amount of hardware you must buy.

Furthermore, my goal is to automate nearly all of this so that, to the extent possible, backups happen in the background without your having to remember anything, press buttons, run apps, or intervene in any other way. And I’ll try to make even the setup process as painless as possible.

Because I want you to understand why I make the recommendations I do and how the whole process works, I spend just a few pages describing my suggested backup strategy in more detail and outlining what choices you’ll make along the way. (If you’re already on board with my basic strategy, you can skip these details and go straight to Choose Backup Software.) As you read, I suggest that you jot down a few notes about hardware that you may want to purchase, software features that seem important to you, or special questions relating to your circumstances to keep in mind as you continue reading the book.

Later on, I provide instructions for every part of the process, so don’t worry if the details still feel fuzzy as you read this introductory topic. I also talk about situations in which this basic strategy requires modifications—for example, when you’re backing up multiple computers on a network, or backing up a laptop Mac while traveling.

Why Create Versioned Backups?

Time Machine and most other backup apps protect data by using versioned backups—that is, backing up your files without overwriting or deleting earlier versions already stored on your backup media. The first time your backup software runs, it copies all your files in their entirety; then, on subsequent runs, it performs an incremental update—that is, it copies only new or changed data. In some cases, incrementally updating a backup means copying each file that has changed in its entirety; in other cases, backup apps copy only the changed portions of files. The latter approach, which I refer to as Delta Encoding, is faster and uses less storage space.

You might be tempted to believe that all those extra versions of your files are a waste of space, but because both humans and computers make mistakes, this type of backup can come in extremely handy.

Let’s say your only backup is a duplicate of your entire disk and you update it every Wednesday. On Tuesday, you accidentally delete a file, but you don’t realize that until Thursday. Too bad: it’s not in your backup, because in the process of duplicating your disk, you also deleted any files on the duplicate that weren’t on the original. Ironically, the more frequently you update your duplicate, the greater the chances of encountering this problem!

Or consider this situation: A buggy app writes some data to the wrong place, damaging numerous files. Again, you don’t realize right away that there’s a problem, and you update your backup. Sure, you have a backup, but it’s a backup of corrupted data!

You may not notice a missing or damaged file for weeks or months. So it pays to maintain versioned backups that go back as far as possible. (For practical reasons, I’d say that a year’s worth is probably enough.)

Although a bootable duplicate includes a single copy of your data, a versioned backup includes many different versions of your data—including, crucially, copies of files that have since been deleted. This makes it much more likely that you’ll be able to retrieve the files you need in the event of a problem. Don’t get hung up on the word “version,” because even if you never need to see a previous version of a file, you may want to see a file that was accidentally deleted, damaged, or overwritten. And, because versioned backups can be updated much more quickly and easily than bootable duplicates (sometimes as often as every time you save, or as seldom as once a day), your prospects of recovering from data loss are much better than with duplicates alone.

You might create your versioned backups with Time Machine. It’s easy to use, and the cost is right: it’s included with macOS. Time Machine isn’t perfect for everyone, though, and I say more about why you might consider something different (and what to choose if so) in Decide Whether Time Machine Is Best for You.

Most people need versioned backups (including those who rely on Autosave and Versions in macOS; see Version Control), but in some cases I can truthfully say they’re unnecessary. If you create very little new content on your Mac, using it mainly to surf the web, play games, or consume streaming content, versioned backups won’t benefit you much. Or, if you do create lots of content but store it mostly in the cloud—especially using services that already store multiple versions of your files, such as Dropbox and Google Docs—then again, having (local) versioned backups may be overkill. But the more you use your Mac to create and store unique information, the more valuable versioned backups become.

Why Create Bootable Duplicates (or Not)?

Ever since I started writing about Mac backups, I’ve strongly recommended that everyone create and maintain bootable duplicates in addition to versioned backups. A bootable duplicate is a complete copy of your startup volume stored on another drive, such that if the startup volume or the drive it resides on ever goes south, you can start up your Mac—or possibly even a different Mac—from your backup drive and get back to work in minutes (instead of hours or days). Bootable duplicates also give you insurance against software updates gone bad. If you install a new version of macOS and encounter compatibility problems, you can quickly revert your disk to the way it was before.

Although that’s still true in principle, the reality has become vastly more complicated in recent years. Apple’s switch to using SSDs as primary storage for most Macs, the introduction of recovery mode and its various iterations, the transition to the APFS file system (starting in macOS 10.13 High Sierra), the T2 security chip, and significant architectural changes in both macOS 10.15 Catalina and macOS 11 Big Sur all changed the calculus considerably. But the introduction of M-series (Apple silicon) Macs represents an even more dramatic shift in how macOS handles bootable duplicates.

The net result of all these changes is twofold. On the one hand, bootable duplicates are far less useful and less necessary than they once were, especially in terms of the primary goal of getting you back to work quickly after a disk failure. On the other hand, it’s become increasingly difficult to create bootable duplicates in the first place, to keep them updated, and to boot from them should the need arise.

For these reasons, I’m now changing my advice. I still explain how to make and use a bootable duplicate, for those who choose to do so; however, because the process has become far more cumbersome for those using Big Sur or later, and worse still for those using M-series Macs, my revised recommendation is that bootable duplicates should be routine only for people running Catalina or earlier (which also implies using Intel-based Macs). Furthermore, anyone whose startup volume uses the APFS file system (see APFS Evolves Further) should use an external SSD, not a hard drive, to store their duplicate, and if you can’t do so for any reason, a duplicate is almost certainly not worth the effort.

Apart from routine duplicates, you may choose to make a one-off duplicate on a special occasion (such as when you’re about to upgrade to a major new version of macOS). But even then, my feeling is that in most cases other types of backup can be suitable if you follow certain guidelines; see Alternatives to Bootable Duplicates.

If you’re content with the summary above, terrific; move on to Why Use External Storage?. However, if you’re curious about the details of all the factors affecting bootable duplicates, read on.

Why Use External Storage?

Hard drives offer the highest capacity of any storage medium plus fast performance and low cost. So external hard drives are the ideal storage medium, at least for versioned backups. (As I explained in The APFS File System, Macs that use APFS for their startup volume should almost certainly use external SSDs, rather than hard drives, for bootable duplicates—if, of course, you choose to make bootable duplicates at all.)

I want to emphasize the word external. Some Mac models can accommodate more than one internal hard drive or SSD (or one of each). And on any Mac, you can divide a single disk into two or more partitions—volumes that look and act like separate disks. Of course, you could put a backup on a second internal drive or on an extra partition of your main drive. But you shouldn’t do that, because if you do, anything bad that happens to your computer could knock out your backup, too. And if you have to send your Mac out for repairs, your backups would go with it. External drives give you some degree of protection against common hazards, the flexibility to use them with multiple Macs, and the option to rotate them offsite (see Store an Extra Backup Offsite).

So, you’ll probably be using an external hard drive for versioned backups, and optionally an external SSD for bootable duplicates, but you still have (up to) four decisions to make:

• Which drive(s) should I buy? I discuss a variety of options (capacity, interface, case design, and so on) in Choose Backup Hardware.

• How many drives should I buy? Having two or more sets of backup media is much safer than having just one. Read Decide How Many Drives to Buy to decide which number is best for you.

• Should I use the drive(s) locally or over a network? If you have multiple Macs, they can all back up to the same drive over a wired or wireless network. Network backups solve some problems but also introduce certain challenges; see Choose Local or Network Backups for details.

• For network backups, should I use a Mac or a network storage device? You can use a hard drive connected to another Mac on your network to store versioned backups for all your computers. Or you can use a NAS (network-attached storage) device. For my advice, see Local vs. Network Backups: Joe’s Recommendations and Network Storage Devices.

Why Use Multiple Partitions (or Not)?

For most people nowadays, I think the path of least resistance is to have an external hard drive for versioned backups, and optionally an external SSD for bootable duplicates.

Depending on the amount of storage you need and what you can afford, it’s also possible to use a single, higher-capacity drive and divide it into two or more partitions (as I describe later in Prepare Your Backup Drive). But, as I explain in Split Backup Disks Are No Longer Great, given that this drive should be an SSD, the cost is prohibitive for most people. For that reason, and because bootable duplicates are no longer as essential as they once were, multiple partitions make less sense than they once did.

Alternatively, a single, somewhat larger SSD formatted as APFS could be used for a Carbon Copy Cloner duplicate with added snapshots, giving you the effect of both a bootable duplicate and versioned backups on a single partition; see Carbon Copy Cloner Tips.

Why Automate Backups?

I can say from personal experience that backups are far more likely to happen regularly if your backup software runs without any manual intervention. And I want to assure you that regular backups are the only kind that matter. I think it’s fair to state this corollary to Murphy’s Law: “The likelihood of suffering data loss increases in direct proportion to the elapsed time since your last backup.” In other words, if you’re performing all your backups manually, the one day you forget (or run out of time) will be the day something goes wrong.

In some situations, you don’t have to do anything special to get backups to run automatically; in others, you have to be careful to set up your backup software to run at a set time.

Why Keep Multiple Backups?

A sound backup strategy always includes more than one backup. Picture this: You’ve diligently backed up your Mac’s internal disk to an external drive. One day, a lightning strike damages both drives. So much for your backup! Even under ordinary conditions, backup media can fail for all the same reasons your hard drive can fail. Having just one backup, in my opinion, is never enough. Most people should alternate between two or more sets of local backup media for greater safety. If you’ve set up your backups to run on a schedule, this might mean using Drive A every day for a week, then switching to Drive B for each day of the following week, then switching back, and so on.

Another good reason for multiple backups is to protect against ransomware, an insidious type of malware that encrypts all the files on your disk and demands a hefty payment for the decryption key. Refuse to pay and you’ll never see your files again. Restoring from a backup made before the ransomware kicked in can solve the problem, but some types of ransomware deliberately wait a few days after being downloaded before they become active, partly to foil daily backups. If you have two backups, one of which is several days or a week old, you’re much more likely to recover from ransomware unscathed. (See the sidebar A Word About Ransomware.)

So, are two sets enough? It depends. To protect against media failure, most experts recommend using at least three sets, of which one is always stored offsite. But using online backups (see Use a Cloud Backup Service) counts as one set, and perhaps as more than one if the provider keeps its own internal backups. If you’re not backing up online, using three hard drives does make rotating media more convenient, as I describe in Use an Extra Hard Drive or SSD.

In my opinion, except for mission-critical business use, it should be plenty to have two separate versioned backups (one of which could be provided by online backups rather than occupy an additional local backup drive), plus an optional bootable duplicate. It’s better to have fewer sets that you maintain diligently than multiple sets that you don’t maintain because your backup plan is too complicated or time-consuming. In any case, if you have more than one set of media, you should keep one in another location all the time. That brings us to the next crucial part of a good backup strategy: offsite backups.

Why Store Backups Offsite?

If someone breaks into your home or office and steals your Mac, chances are they’ll also grab whatever’s attached to it, such as your backup drive! Fires, floods, earthquakes, and other disasters could likewise wipe out your backups as well as your computer. As much as we want to believe these things will never happen to us, the prudent course is to plan as though they will. So I urge you to keep at least one copy of your data far away from your computer. You have quite a few choices, including physically moving hard drives from place to place and using an online backup service; I outline the options in Store an Extra Backup Offsite.

Online backups also provide extra protection against ransomware. Even if a malicious app encrypted everything on your Mac and on mounted external disks, it couldn’t affect backups already stored in the cloud. (Again, see the sidebar A Word About Ransomware.)

Can Cloud Sync Simplify Backups?

Speaking of storing data online, you may be thinking, “Hey! I use Dropbox (or iCloud Drive or Google Drive or any of a zillion other cloud storage services) already. Doesn’t that count as an offsite backup?” Not necessarily; I explain why in the sidebar Dropbox Kinda Sorta Offers Backups. However, cloud sync absolutely can simplify your backups! More specifically, it can simplify restoring your data, especially when you’re moving to a new computer or a replacement hard drive.

I was discussing backup and restoration strategies with a reader, and he asked me exactly what I’d do if my Mac’s startup disk died and had to be replaced. In particular, he was wondering how I’d deal with the differences between my last bootable duplicate and what had been backed up more recently by Time Machine or an online backup service (see Finding Recently Backed-Up Files).

I told him I’d restore my disk from the duplicate, which would get me pretty close to my disk’s last state because I update my duplicate twice a day. But then, realistically, I probably wouldn’t have to touch my versioned backups, even if they were hours or days out of date. That’s because nowadays I store most of my important day-to-day data in the cloud.

Personal data such as email, contacts, calendars, reminders, notes, browser bookmarks, and photos sync automatically thanks to iCloud and other services. And most of the files I work on regularly are stored either in iCloud Drive or in my Dropbox folder. So merely starting up a Mac on which the relevant apps are installed and logged in to their respective accounts will make most of my personal data automagically update itself to the latest versions. If I noticed anything missing, I could always fetch it from a versioned backup later, at my leisure.

I’m not saying that cloud-based data storage and syncing is a substitute for backups, but rather that when the cloud contains the “master” copy of your important data, you can often skip a number of tedious steps when it comes to restoring backups, because the most crucial data syncs all by itself.

So, both to simplify data restoration and to make your life easier when working with multiple devices, my recommendation is: use IMAP for email if you don’t already (see my article FlippedBITS: IMAP Misconceptions); use iCloud or a comparable service for syncing data such as contacts and calendars; and use iCloud Drive, Dropbox, or any of numerous similar services for syncing your files to the cloud and across computers. And, crucially, adjust your habits so that your most frequently used files are stored in a location that syncs automatically to the cloud.

Can You Reduce Your Backup Footprint?

If you’re making a bootable duplicate, you’ll almost invariably want to copy every single file from your startup volume. With versioned backups, however (whether stored locally or in the cloud), you may want to reduce the volume of data you’re backing up in some situations, such as these:

• You’re stuck with an external hard drive that’s smaller than what you should ideally have (see Decide on Capacity).

• You’re using a cloud service that charges by the gigabyte and you want to economize as much as possible.

• Your external drive or broadband connection is slow, meaning backups take longer than you prefer.

One approach to this problem is to be selective about what you back up; for example, you may exclude certain extra-large files for which having multiple copies isn’t crucial (see Exclude Files from Time Machine). Another approach is to reduce the total amount of data on your Mac in the first place.

Getting rid of unneeded files can address numerous problems besides backups. It can reduce software incompatibilities, simplify software upgrades, and keep your Mac from running out of disk space (which can also slow it down). Here are a few quick tips:

• To configure Optimized Storage options, which can reduce the amount of disk space used, go to System Settings > General > Storage (in Ventura or later) or choose Apple  > About This Mac > Storage, then click Manage (in Monterey or earlier). In particular, consider clicking Optimize and (after confirming) selecting both checkboxes to permit macOS to remove movies and TV shows you’ve already watched, and email attachments, from your Mac. (You can always download them again later if needed.)

• Try an uninstaller utility, such as CleanMyMac, which can also find large and old files you might want to delete.

• Eliminate duplicate files using a utility such as Gemini 2.

• Be sure to empty the Trash (in the Finder, choose Finder > Empty Trash) to recover disk space after deleting files.