Time Machine completed a verification of your backups. To improve reliability, Time Machine must create a new backup for you.

Ok, it has been two months now since I have last had this error message.

What I did was to turn OFF WiFi on my iMac so that my Mac is connecting to the TimeCapsule via ethernet ONLY.

This is the way I had always run it without problems ( for years ) I had only turned on WiFi when Sierra came out so that I could unlock my iMac with my Apple Watch.

I hate to be pessimistic, but this is probably as much related to the problem as turning the lights on and off. I never had a Wifi connection to TC and still got the problem. This is a bug in Time Machine that Apple is apparently unable/unwilling to solve

I also have this issue. On my MacBook and my fathers MacBook both running Sierra.

We use two NAS, FreeNAS and Rockstor.

This would indicate that its an issue with Sierra itself rather than Time Capsule or other NAS products.

You can speed up Time Machine by using typing this into Terminal:

sudo sysctl debug.lowpri_throttle_enabled=0

That will disable throttling until you reboot and makes Time Machine run faster, it will use more battery though. It's a good way to speed up a large Time Machine backup, especially when you have to create a new one.

The problem seems to have been quietly fixed, for Sierra anyway. I haven't seen a failure in what must have been months now, and I did not change anything new. This did happen to me very rarely before Sierra, and I wouldn't be surprised if that continued, but the daily/weekly failures seem to be gone.

I hope its fixed now, here's my experience anyway:

I had this problem after installing Merlin firmware on a Asus RT-AC56U router.

The asus has a time machine option --after a few days it would fail verification.

I then returned to using my time machine on my old airport extreme and that started failing verification also (this had never happened before)

Next I tried qnap NAS time machine, it started failing verification.

The common piece of hardware was my MacBook was still using wifi through the asus router to reach all of these.

I flashed Advanced Tomato firmware on the Asus and have been running for 5 months without a verification error, and can backup to anything (Asus router, airport extreme, Qnap)

Right now it looks like my problem was a wifi router problem, specifically something in the merlin firmware. I never ran the stock asus firmware long enough to test it.

I love the Merlin firmware so I tried switching back to it and immediately (on first backup) started having backup failed and would not even finish.

Switched back to tomato and no problems.

Not sure if other people are using a different wifi router or not but something to look into.

I switched mine because I wanted an AC router.

--This same message and problem occurs about once every 6-12 months for me. Each time, Apple Time machine says my Time Machine data is not usable, and gives me no option to rebuild the old data file, gives no error message to help track down the problem, and demands the backups start over from scratch, dropping all access to the old backups.

--It is a black eye for Apple that the Time Machine system appears to use a fault intolerant data file, provides no way to recover from whatever the problem is, gives no error messages to trace down the source of the problem, and has let this situation exist since at least 2012.

--Apple backup system is not for professional applications, and in a way is worse than no backup since it gives a false implication that I have a backup that I can rely on.

I note all the people playing with wild ideas that it is related to some software or hardware in their system. Well, maybe it is, but I suspect they are being mislead and do not see the depth of the problem with Apple Time Machine. In my case, with crashes occur once over 6-12 months, over a 4 year period, through a variety of Apple OS updates, how am I supposed to track down the problem?

--Why no error report when we are talking about the loss of a terabyte of data?

--Why no recovery scheme? Why toss out a terabyte of data without any effort to let the user recover and debug the problem?

--Why can just one error destroy an entire terabyte of data? Data file was fine yesterday, today one unknown error occurred and the entire file is gone. A file of this size and importance should be bulletproof and recoverable from a multitude of errors, at least in part.

That Apple has not addressed this angers me and makes me roll my eyes at those that say Apple systems "just work." How oblivious they are.

-->In a professional world, repeated failures of this magnitude would never be forgiven.

As you can surmise, the problem is arising again and I am at a loss as to what to do about it.

That Apple has not addressed this angers me and makes me roll my eyes at those that say Apple systems "just work." How oblivious they are.

-->In a professional world, repeated failures of this magnitude would never be forgiven.

I feel your pain. They are losing the plot, methinks. I tried to delete an old backup file off a portable disc the other day.... complete nightmare.

I hardly come to these support communities now. They used to be well laid out, easy and logical to navigate.... now the "too cool to breathe" presentation makes the place an unwelcoming pile of doo-doo. Mr Cook should focus on making Apple "just work" instead of promoting his unpopular politics.

Same issue here, using a Time Capsule. Took about a month to complete the initial backup, and then got the message about making a new one. At this point I consider Time Machine to be a bonus if it were to happen to work, but would NEVER depend on it.

My best use case for Time Machine is when migrating to a new laptop. It doesn't seem to work as well for locating single files that have been corrupted, or mistakenly deleted. I have added an online backup service for my photos and documents, and that makes me feel much more secure. I guess that's good backup strategy anyway -- multiple copies in multiple places on multiple media.

I've had at least five of these kinds of TM errors on my Synology 1515 NAS since I bought the thing in June. Both in El Cap and now Sierra, although it seems to be worse now. I'm new to NAS and bought the thing because I have about 10 TB scattered around different drives and I wanted them in a unified TM backup because it's a pain otherwise. Trying to triage it with exceptions to fit on hocketed 8TB TM drives has been expensive and inefficient, as I still had to do manual backups of some of it. I really need drives of 12-14TB to do single-drive TM properly and they don't exist.

Also, I had a lot of problems with 8TB drives going bad. Synology's SHR2 striping allows 2 drives to fail, so I figured this was a good solution for TM. 5 bays x 8TB with all the striping still gave me a lot of breathing room at 23 TB. I figured that was safe. I figured I'd get a couple of years of TM backups without worry.

I thought wrong. As good as Synology NAS devices are, they can't protect one from corruptions caused by un robust software from apple.

The first couple of times when the errors occurred, I was successfully able to use Disk Warrior and/or the lengthy terminal process outlined in the article earlier in this thread to repair the .sparsebundle drive image. But the last two times, this has not worked. I have used the NAS both over wired Ethernet and over wifi. It doesn't seem to matter, as the errors occur either way. So then it's off to reformat the NAS and do a shiny new backup which takes tens of hours, yet again, and again my incremental backup history is hosed. I have no backup history since June.

I do also use Backblaze, but it has its limitations, I was hoping to have another way to access TM files remotely, I have now spent dozens of white-knuckled hours on this vexing issue and I've had it.

Until and unless Apple fixes this NAS/TM corruption, the only solution I'm coming up with is to abandon NAS and buy a wired Drobo or other wired enclosure with RAID 6. And that's probably my solution.

As the history of Time Machine and NAS's is rather checkered (they have gone from unsupported to poorly supported) I see no reason at all to recommend or even suggest one, failure is the common end result and I will continue to tell the people who come here to tell us that their NAS does not work why it does not work reliably.

Bob Timmons wrote:

You told us that NAS drives are not supported. This is not correct. I have used one for the last few years.

You are entitled to your own opinion about network drives, but not to your own facts.

The support is very poor, as witnessed by the fact that this forum is littered with posts from people whose backup to a NAS is unreliable. An unreliable backup is no backup at all.

I am backing up to a Time Capsule, and have just started to get the same error-

iMac 2017, Mac OS 10.12.6, latest Time Capsule 3GB

Just got a new RAM module installed because the last one failed- since I got it back, it has thrown up this message overtime I try to back up.

Weirdly, I can enter access my Time Machine backups through the timeline - but it just won't back up anymore.

I also use the same Time Capsule to back up my MacBook Pro- and have had no issues with that machine.

AppleCare was unable to help, and advised me to delete my existing backup, and start a new one- but my Time Capsule holds valuable past versions of academic papers, so I would take hours to pull them out first.....

Anyone had any luck with a fix yet??

I'm using Time Capsule with an external USB drive hung off it. The internal drive is for my wife's laptop and mine is supposed to back up to the external drive, but it's been months since Time Machine was functioning.

Based on the above post, I tried disabling PowerNap. In an apparent effort to be really unscientific, I also did a hardwire connection to the backup drive to speed up the initial backup, which after weeks was still "waiting to complete" over wifi. Then after that was done (took overnight) I hooked the backup drive back to the time capsule and set up TM to back up to that drive.

I'm not sure if the PowerNap disable or the hardwire initial backup solved it (or perhaps the 10.13.2 MacOS update?), but after 4 or 5 months Time Machine is finally working again over WiFi!