Time machine must create a new backup - all the time

Hi all, I am regularly getting the message

"Time Machine completed a verification of your backups on . To improve reliability, Time Machine must create a new backup for you. (Then I have options of 1) back up later or 2) delete existing backup and start anew.

This is defeating the whole point of Time Machine as I keep having to delete the entire Time Machine backup.

I’m currently on Mojave and about to step up to Catalina but I will use Carbon Copy Cloner first. The backup is a Netgear ReadyNAS, connected by wired ethernet to my airport extreme and then I connect wirelessly to that. I can connect wired as well relatively easily. Anyone else experiencing this or know a cure?

I saw this problem frequently on multiple machines before upgrading to Mojave. It’s maddening. I haven’t had it since then but from what you’re seeing it sounds like I should expect it to pop up again at some point. My configuration is Ethernet to a Synology NAS.

I’ve heard many others complain about this aspect of Time Machine reliability. Some solved the problem by switching to a wired connection (that didn’t work for me). Others say that Time Machine doesn’t work well across a network and recommend a directly connected drive. Maybe? That’s not really an option here and so I’m planning to switch to some other software instead (probably either Arq or Chronosync) when I upgrade my aging NAS. Any day now…

I keep multiple CCC backups as well. It seems to be much more reliable than Time Machine.

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I gave up on Time Machine and now use a combination of Backblaze plus a nightly snapshot using SuperDuper!

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Clones and Time Machine have separate purposes. A clone helps you get up and running immediately if your main disk dies, Time Machine helps you recover previous copies of files. In the past I have recovered a dead disk from Time Machine, it just takes a long time.


Have you successfully backed up using your current configuration in the past?

Yes but after a few backups it says does what I said in the first post.

I had this error all the time and replaced the hard disk, as I presumed that was the reason. Since then, it’s not occurred in months.

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I stopped using TM directed to a NAS (Drobo) device on my network. Problem stopped. Changed to USB connected devices. I backup to two connected drives. No problems at all.

As I think back before that, the only problem I’ve had with a USB drive was when one of the drives was failing. Unable to even “repair” with the Disk Utility. Replaced the drive with a new (and bigger/cheaper one) and all well.

I use two TM USB drives on both my Macs.

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TM backups across a network are very prone to toasting themselves, somewhere on here there’s a thread I created having stumbled into the same issue.

I’ve noticed that a key contributing factor was if I closed the MacBook lid putting it to sleep while a backup was in progress. I don’t think it recovers very well (sometimes: not at all) from an interruption to a wifi connection.

To reduce opportunity for problems I’ve turned off the TM option to backup on battery power, if I’m planning on closing up the MBP shortly I unplug it from the power & that stops it from initiating a backup. If I’m on power I’ll check a backup isn’t in progress before closing the lid.

I don’t reboot my NAS while a backup is in progress, did that once, backup went kaboom, didn’t do that again!

I have mine set to back up automatically, the more frequently it backs up the smaller each back up run, the less chance for issues. (I’ve noticed really large backups can get stuck although so far it’s recovered ok from each of those).

If something has happened that will cause a large back up ( OS update / Adobe Apps updating themselves) then I’ll try to do the next back up over ethernet rather than wifi. This is mainly a speed / convenience thing. While my wifi connection is quick in overall data through put, wifi seems to have a “random access time lag”, I’ve recently had painful experience of this with Windows RDP sessions too.

TM backups to Direct Attached Storage are a lot more stable so in TM I added another disk and every few days connect a USB drive. This gives me a balance between a backup that happens automatically but might shoot itself in the foot vs a backup that’s more stable but requires manual action to instigate.
Ideally I’m hoping Apple sorts this out so it becomes a backup that happens automatically and doesn’t shoot itself in the foot!

Hope some of this helps you! :slight_smile:

Yes, had this many times myself. Even from my iMac Pro to my Synology over a wired connection, and with the iMac always on.
Currently I do:

  • Arq 5 backup to MinIO on the NAS.
  • TimeMachine to external drives that I replace every year.
  • Backup of research data to drive I rotate off site every 15 days (off site being to my car in the driveway since COVID-19).
  • Continuous backup to Backblaze.
  • Daily backup of my research data (with archiving) using ChronoSync to an external.
  • CarbonCopyCloner bootable backup to SSD monthly.

Time Machine is known to work well with locally-connected USB drives, Time Capsule, or Time Machine server (e.g. a Mini running the server software). Other than those, not so much. I wish Apple would put a little effort into making it more universally reliable, especially with NAS’s, but they have shown no inclination to do so :frowning_face:

There is a free utility called TheTimeMachineMechanic. I haven’t used it much so I don’t really know if it would help. The publisher of this software, eclecticlight.co, has a lot of deeply technical information about Macs and Mac software, including Time Machine.

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I have had better results with Time Machine backing up to a Mac Mini with external storage. No failures. I also use 2 locally attached drives, one for Time Machine and one for CCC. All my pictures and files are also kept on iCloud. Finally I have ArqCloud for the apocalypse scenario.

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Update: I got my Time Machine NAS running again and it took 20 hours to back up 1TB. It has 4 x 2TB spinning drives for a total of 8TB and I got it for my previous Mac which had a 2TB internal hard disk - 2x for Time Machine and 2X for redundant RAID.
My current MBP has a 1TB internal SSD and a 1TB external SSD for DSLR photos, so the Time Machine size would have to be at least the same.
The NAS lives in the basement and has a wired or wireless connection to my MBP. It’s in the basement due to being noisy as well as taking up desk space and needing power and an ethernet connection. I like to minimize cables on my desk as much as possible.
I’m thinking a Thunderbolt replacement with SSD could be smaller and quiet enough to keep on my desk, as well as fast enough to do the backup in minutes rather than hours. Any suggestions?

The apocalypse I used to worry about was the one where a giant solar flare kills everything electronic, after we have digitized everything…

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I use a Sandisk Extreme Portable SSD which is USB-C rather than TB3. It is indeed quick although for your initial backup I would think you’re still looking at hours rather than minutes. In my instance at least, incremental backups are usually only a few minutes though. Due to it’s speed I’d definitely recommend that if you can afford it.

Generally, it seems to be recommended that your TM backup disk is twice that of your storage, so in your instance that’s 4TB. For SSD storage that is going to be hugely expensive! (If you can find an SSD that big, I think the Sandisk ones like I have only got up to 2TB).

From (bitter) personal experience I’d suggest getting as large a backup disk as you can. I had a 500GB disk & wanted to switch to a 1TB when it got full. I had a load of problems moving the TM backup from the old disk to the new and in the end gave up and just started over with the new disk. As far as I can work out this is an issue with they way TM uses symbolically linked files to save space.

I’ve heard quite a bit of discussion in podcasts / YouTube and so on about buying internal SSD drives and putting them into TB3 or USB-C enclosures, that could be an option worth exploring.


I gave my Mac a wired connection and had no trouble from Time Machine. But I “only” have 2 ethernet sockets on this side of the room, and I’m working at home with 2 other computers both of which need wired connections because our wifi stops and restarts starts regularly (AirPort Extreme with more or less line of sight connection to the 3 computers). So My Mac had to give up its wire, and pretty soon the Time Machine failures started again.

I found these 2013 links about Time Machine not working over WiFi:


I’m wondering if there’s a way to tell Time Machine to only work when there’s an ethernet connection and not when on wifi. I could also switch to a local bus powered drive for Time Machine and/or figure out what’s wrong with the wifi…

How about attaching a 2- or 4-port switch to one of your existing ethernet sockets?


You could do this with Keyboard Maestro, but @jec0047’s suggestion of a switch is probably less painful.

To enable TimeMachine backups, use this command (from your keyboard maestro macro):

tmutil enable

You can probably guess the command to disable :slightly_smiling_face:

ps. If you need to be super user, this will do:

sudo tmutil enable
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