Best Disk Format for Time Machine on Monterey

Which is why it’s aways a good idea to back up to multiple disks. This is of course true also for HDDs.

Every disk (SSD and HDD) will eventually fail. You can knock down probability of that happening to some extent by buying serious hardware and keeping things reasonably up to date, but what you really need to do is make sure you have a plan B when that does happen. A second (and third, fourth, …) backup disk is invaluable as such.

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Good points Simon. It is possible to use data recovery services to reclaim data off a failed HDD but not off a done SDD.

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I have no personal experience, but DriveSavers says they can recover data from an SSD. I once toured their facility and they can do some truly impressive stuff.


DriveSavers is a pretty decent data recovery service, but they are very expensive.

I’ve seen enough data recovery videos from iPad Rehab and Louis Rossmann that I don’t think their services are unique or worth the prices they charge.

That having been said, data recovery will always be a significant expense, no matter where you go. It’s always better to have backups so you don’t need to recovery anything in the event of a failure.

A less expensive first step would be to try SpinRite by GRC (Steve Gibson). Often very effective, and may be all you need. (Current version needs to run on a PC, but next version will boot on Intel Macs)

Robust it may be, but apparently, there are some edge cases in which Time Machine using APFS (TMA) can eat up a lot of disk space and thereby make it a poor choice:

For the great majority of users, snapshots are a valuable enhancement and cause no problems. But for a few, if they’re not carefully managed, they can eat so much free space that it affects their work. Instead of just deleting them, you need to discover the cause and address that. In a very few cases, it could mean that using snapshots as part of your backup strategy isn’t a good idea, in which case Time Machine isn’t a good choice. Thankfully, such cases should be rare.

This is far more important for local snapshots (of your Data volume), where large temporary files may consume a lot of space you would rather be freed. But those snapshots will self-destruct in 24 hours.

Snapshots on a TM volume are not the same, because the same files will cause a TMH volume to retain the storage. The fact that it TMH does it with many hard-links to a file instead of with snapshots doesn’t really change anything unless you decide to start manually deleting individual files from within your a TMH backups.

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Indeed, Howard Oakley says as much in today’s post:

Which ends with this advice:

There’s an important lesson for us with respect to apps which make snapshots, like Time Machine and Carbon Copy Cloner. Where you have large files which change a great deal but don’t need to be backed up as frequently, don’t simply exclude them from your backups, but put them on a separate volume which doesn’t have snapshots taken. This could apply to folders of temporary and cached data, Virtual Machines, downloads perhaps, even databases and Photos libraries. There’s something to be said for a user-equivalent to the hidden VM volume.

Yes. But this advice about large files applies to any backup strategy that maintains historic backups, whether or not snapshots are the mechanism used.

For myself, I keep a folder (aptly named ~/Not backed up), which is on Time Machine’s exclude list. I keep in there things like VM disk images and my Audacity projects, which would consume a lot of space if part of a TM backup. These files only get backed up when I make clones with CCC. This way, they don’t cause premature clobbering of TM history due to snapshots consuming too much space.

Yes, they may result in my CCC backups not maintaining as much history they would otherwise, but I usually don’t care about historic data on those backups beyond maybe the last month or so.

And my backup drives are plenty big (2x the total capacity of my Mac’s storage and almost 3x the size of my data), so I’m really not too worried about it.


I have a MacBook m1 and I use an external HDD spinny drive for time machine. I have it formatted as APFS and I find Time Machine terribly sluggish. My computer is amazingly fast though. My connection is USB3. It’s a Seagate drive with 8TB. A few months after getting my mac, I noticed that time machine wasn’t backing up. I could see the data on the drive. I could not get time machine to work. I ran disk utility and it said there were errors that could not be fixed. I immediately took another drive and ran time machine on it all night long. It successfully backed up. I don’t remember the exact order of events, but I contacted apple support. They didn’t know what to do. They said there was no other way to fix the first drive without erasing it. I did, knowing I had a fresh time machine backup. After erasing the drive, it would no longer mount. Additionally, after plugging in my fresh backup, it also would no longer mount. I could see the drive container in Disk Utility but couldn’t use first aid, couldn’t erase and couldn’t mount. I got a brand new 8TB drive and it’s been backing up fine for a couple months and then yesterday I got a notification that it had not backed up in 28 days. I forced a backup, which started off saying it was going to take 2 hours and ended up taking about 12. It did complete. I ran disk utility and I’m getting the same error message that I got the first time.
I’m just wondering if APFS should not be used on the spinning drives. Or if my drive is actually Ok and disk utility is wrong? Is there another disk utility application that I can use to test it? Should I change the format back to HFS+? I realize that I lose the data if I do this.

  • Performing fsck_apfs -y -x /dev/disk4s2
  • error: container /dev/rdisk5 is mounted.
  • Storage system check exit code is 65.
  • Storage system verify or repair failed. : (-69716)
    So, I tried time machine and it does work, but as I started this message, it is very sluggish. When I try to go back in time, the window goes dark grey and empty for about 5 seconds and then snaps to the new date. Gone is the nice animation.

Your problems are not likely related to APFS per se. Apple recommends APFS for TM backups for any macOS since Big Sur. That recommendation makes a lot of sense, just see Howard Oakley’s articles I linked to at the very top of this thread. There is for HDDs indeed a performance penanlty related to APFS use vs. HFS+, however, that penalty usually does not apply to disks used for TM backups. And of course, your issue is not performance but reliability.

Disk Utility does have a bug in that it claims it cannot fix a backup disk, when actually it just cannot properly unmount all the backups on that disk first. So what you really need to do is use Disk Utility on your TM disk in Recovery Mode. Do that first to confirm if indeed there’s an issue with your disk. More details below.


But note also that, according to the Eclectic Light blog posts, the problem seems to be with the Disk Utility GUI tool, not the underlying fsck_apfs utility that it calls under the covers.

The problem is that Disk Utility won’t umount/remount the Time Machine volume and all its snapshots, so it can’t perform a normal check/repair. And it doesn’t pass-in the -l option that is required to check (without any repairing) a “live” volume.

If you’re comfortable with the command-line, something like this should work:

$ sudo fsck_apfs -n -l /dev/disk4s2

Note that it will take a very long time to run, because it will check all of the volume’s snapshots, and Time Machine will have one for every backup stored on the volume. So it may take several hours or even days to complete. And if it finds any problems, it will report them but will not attempt repair (because the volume is still mounted).

If it finds problems and you want to attempt repair, you should boot into Recovery mode and run Disk Utility from there. Without TM running in the background it should work. But again, it will take a long time to complete, due to all the snapshots.

You can speed up the process using the -S option (telling it to not check the snapshots), but there’s really no point in doing that on a Time Machine volume. The snapshots are the entire reason for the volume’s existence - if you don’t check them and there’s an unreported problem as a result, then you’ll have a corrupted backup and not know it.

Regarding comparing HDD vs SSD for Time Machine on APFS:

SSDs should be preferred over hard disks for storing Time Machine backups on APFS. Hard disk performance and working life are seriously impaired when APFS is used.

Yes, SSDs have massive performance benefits over HDDs when APFS is used, but Time Machine is a special case scenario. IMO, the performance difference really doesn’t matter for most people because:

  • TM backups run once per hour, and in the background. As long as an hourly backup completes before the next one starts, who cares if it finished in 5 or 10 or 15 minutes?

  • APFS’s ability to create massive fragmentation is somewhat mitigated by the fact that it isn’t randomly modifying files. It creates a snapshot and then writes the files that changed. So changes tend to be localized near each other. Even though periodic snapshot deletion (hourlies after 24 hours and dailies after a week) does create fragmentation, it’s not going to be nearly as much as you might see on an HDD used as a boot device or for document storage.

  • The price difference is likely to be more important to those of us on a budget (almost all of us), especially when the use-case is backup and not for working files.

    For example, a 2TB SSD costs $130-280 (from MicroCenter). Looking for an external HDD for under $150, I found a 6 TB drive). Looking for an external HDD for under $280, I found a 16 TB drive).

    The ability to get 3-8x the capacity for the same price, especially for an application where performance is not critical, is not something you should ignore when making purchasing decisions. (Of course, you should still research each products’ reliability before making a purchase and not just look for the lowest price/TB ratio. This is true for both SSDs and HDDs.)

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As I understand Howard’s reply, the cumulative fragmentation caused by file deletions within snapshots becomes significant after an extended period of time.

As much as I respect Howard’s insight, knowledge, and recommendations (I’ve cited/referred to him quite a few times here on TidBITS), my experience with using hard drives formatted with APFS is not consistent with what he’s saying currently. I’ve been using two 4TB hard drives formatted with APFS for TM backups, and two other 4TB hard drives for CCC backups, for nearly two years. The CCC backups are considerably faster than when the drives were formatted for HFS+, and the TM backups have not given any indication of any significant slowdown (and in fact, seem to be somewhat faster) in that period of time. None of the drives show any indication of excessive fragmentation (though perhaps they have more than when HFS+ formatted).

I also don’t agree with his stated expected lifetime of a hard drive as being 2-3 years, a timespan that in my experience, is ridiculously low: several of my drives are at least 10 years old yet are doing fine. I’ve had three drive failures in the last 20 years. I feel I have sufficient redundancy (two independent backup systems, not counting an online backup, using alternate backup drives) to account for the inevitability of future drive failures. In all, I have 12 hard drives in use across the four systems I’m responsible for. The drives used for file storage (11TB of media files) are formatted HFS+. The drives used for backup (TM and CCC) are formatted APFS.

I don’t think a 1TB drive, or even 2TB, is adequate for backing up nearly 1TB’s worth of files. 4TB SSDs are still obscenely high in price and likely to remain so, notwithstanding what is now many years of being on the market. So I’m supposed to replace (in my case) at least four 4TB hard drives with some clutch of 8 to 16 SSDs with their far inferior price/TB ratio when the hard drives are still performing well? I don’t think so.

All above assume “low speed” SSDs (SATA/USB 3 etc). Howard mentions his hopes for prices of Thunderbolt front end SSDs to come down. I have the same hopes, but the truth of it is, Thunderbolt SSDs are 8x or more the prices of their USB 3x counterparts, and given the fact that we’ve been waiting for Thunderbolt prices to come down since the intro of Thunderbolt 1, we’re going to be waiting for a long time to come. I fully agree with Shamino’s recommendations regarding price/storage ratio.

I’m still a huge fan of Howard’s and consider him at the top of the heap in Mac expertise. His contributions to the community are immense and ongoing. However, there is a small subset of items where my results seem to vary a bit from his…


Maybe so, but even he says that this ultimately boils down to performance. And for something like Time Machine, performance really isn’t critical, as long as each backup completes before the next one is scheduled to begin.

But I would suggest looking for a high performance HDD. A small 2.5" portable drive is not going to perform anywhere near as well as a 7200 RPM 3.5" drive designed for 24x7 server operation (e.g. a “NAS” or “Enterprise” drive).

You may have to build your own external drive in order to get this, because most sold-as-external drives have slower consumer-grade drives in them. But that shouldn’t be a problem - it is very very easy to buy a bare drive and a USB enclosure and mount one in the other.

I’ve experienced the same thing.

I assume this is because the act of creating and deleting snapshots is much much faster than creating and destroying hard-links to duplicate files/directories (for TM) or moving files to a SafetyNet folder (for CCC), and not because of the nature of APFS itself.

But for a user (vs. a kernel developer), the reason for the better performance doesn’t matter. The fact that the APFS backups perform faster is all that matters.

I don’t believe for an instant that this observation would hold true for a general purpose volume holding actively-used apps and data, but backup media has a use-pattern that is very different from general-purpose access.

It also helps to have backup drives that are substantially larger than your source drive(s), so thinning doesn’t happen for a long time. In my case, my internal SSD is 2TB, of which the Data volume (that gets backed up) is about 1TB. I back it up to a 4TB HDD which currently has backups going back to May 11 (7 months - when I wiped it to switch from HFS+ to APFS) and has 2.6 TB available.

Please tell me more. I have noted in other threads that Time Machine has become wonky after two recent upgrades to macOS, and I think (without certainty) that an attempt to backup to my Time Capsule might well take over an hour (at which time a new snapshot should presumably begin).

On the other hand, Time Machine backups to an external spinning HDD take under an hour and they still fail, so it is probably something unrelated to a new backup colliding with a backup in progress.

One other thought. I believe, back when my TM backups worked, that the time shown for the most recent backup was the completion time of the backup. If this is the case, then it seems like the “next one” would be scheduled for an hour after the last one completes, and there could never be a collision.

I’m not sure what else I can add, but some possibly useful points:

  • A Time Capsule is not like a directly-connected storage device. It is network storage. As such, TM will back up to a “sparse bundle” disk image. This image may be (I think) formatted as HFS+ or APFS. I don’t know which is used by modern macOS installations, but if it is treated as locally-attached storage, then it is determined by the version of macOS that created it. Catalina and older creates HFS+ TM volumes, while Big Sur and later creates APFS TM volumes. If you created your TM volume as HFS+ (with an older macOS), it is not upgraded to APFS, but remains operating as an HFS+ TM volume until you decide to delete and re-create it.

  • I’m not surprised that a TM backup to a Time Capsule takes longer than to a local HDD. USB3 has a higher theoretical top speed (5 or 10 Gbps, vs. Ethernet’s 1Gbps), and network protocols like SMB are going to have more overhead than something like UAS, which most good quality USB3 enclosures support.

  • TM’s reliability seems to be different for different people. I never had a problem with it on my systems, although I did experience the bug (on Catalina, I believe), where it would stop making automatic hourly backups after a few days of uptime. I worked around this by manually telling it to run a backup whenever I noticed it hadn’t run for a few hours, which seemed to get it working properly for the next 2-3 days.

    My current Mac (running Big Sur) hasn’t given me any problems.

  • No, there can never be a collision. If a backup is running when the time comes for another, then the new one doesn’t happen (or gets delayed, I don’t know which). My point was simply that you don’t need backups to complete very quickly, as long as it’s fast enough that your hourly backups remain approximately an hour apart.

That’s what I would have assumed, but it seemed like you implied otherwise.

I understand (and agree) that performance is not a high priority, and that using a Time Capsule includes a lesson in patience.