Time Machine hangs up on "Preparing Data"

You need to do a factory reset of the TC.. and a completely new configuration.

Let me recommend the following.

Factory reset universal

Power off the TC.. ie pull the power cord or power off at the wall.. wait 10sec.. hold in the reset button.. be gentle.. power on again still holding in reset.. and keep holding it in for another 10sec. You may need some help as it is hard to both hold in reset and apply power. It will show success by rapidly blinking the front led. Release the reset.. and wait a couple of min for the TC to reset and come back with factory settings. If the front LED doesn’t blink rapidly you missed it and simply try again. The reset is fairly fragile in these.. press it so you feel it just click and no more.. I have seen people bend the lever or even break it. I use a toothpick as tool.

N.B. None of your files on the hard disk of the TC are deleted.. this simply clears out the router settings of the TC.

Setup the TC again.

Then redo the setup from the computer you want to use for TM using Airport Utility.

1. Use very short names.. NOT APPLE RECOMMENDED names. No spaces and pure alphanumerics.

eg TCgen5 for basestation and TCwifi wireless name.

If the wireless is still a problem set wireless names like TC24ghz and set the 5ghz to different name.. eg.TC5ghz

2. Use all passwords that also comply with 1. but can be a bit longer. ie 8-20 characters mixed case and numbers.. no non-alphanumerics.

**3. If the TC is main router you can skip this point. This is only an issue when the TC is bridged.

Ensure the TC always takes the same IP address.. you will need to do this on the main router using dhcp reservation.. or a bit more complex setup using static IP in the TC.

Ignore this point if you don't understand it .. post back if you have drop out issues.

4. Make sure IPv6 is set correctly in the computer. ie link-local only for ethernet and/or wireless depending on which you use. Auto is not good enough.

Once you complete the above..

Reselect the TC as your backup target in TM setup.

TM will say it is going to create a new backup and start in 120sec.

What it will do is discover the existing setup and do a check of it.. if the old backup is verified as OK TM will continue using the existing backup.

Be warned if the existing backup is corrupt TM will delete it and start over. Sometimes it is necessary to actually delete the old backup to get things going again. If the old backup is important to you .. archive the TC to a USB drive before you do a full erase and start over.

Please read a few of the notes from Pondini. Old but still helpful.

http://pondini.org/TM/Troubleshooting.html

A4 and A5 on reset of TM and verifying backup and drive.

B5 and B6 on reconnecting to your backups.

IMHO it is simply better to start a fresh clean backup.

TM is also less and less reliable to network drives.. if you want a reliable backup then buy a self powered USB drive .. plug that into your computer.. partition it in two and use Carbon Copy Cloner to make a bootable clone on the first partition and use TM on second partition. This is going to be faster, far more reliable and cheaper substitute to a new TC which is otherwise most likely needed.

If your TC is more than 3years old it can simply need replacement.. they do die before that fairly often so if your is AC version don't be surprised.

Archive off all the existing backups. Start fresh backup. In the end you need to kick start it and that is often what is required.

The TC older than 3 years should just be replaced. They become unreliable.

You must verify local disk.

Did you load any software recently into the computers.. security or anti-virus software on a Mac causes huge problems.. it will typically not work with Time Machine.

The computer should backup directly (over wireless or ethernet) to the TC. Not via any other router in your network.

No luck with any of this.. well I recommend you do a backup to a USB drive plugged directly into the computer. That way you have a viable current backup and can work out if Time Machine is having issues due to corrupt files on the local computer. TM works a lot better to local drives.

And I would buy a 3rd party backup software like Carbon Copy Cloner and use that. Since about Mavericks we have seen the number of TM issues go up and up and the TM backup is much harder to work from than a direct clone. CCC can also backup to your TC. It is not over expensive and provides a way around your problem.

It sounds like you have setup a folder under an identically named folder.

TM must work in the main folder of the TC .. it cannot put files into a secondary folder..

And you did not create the main folder named data.. that is default configuration for every Time Capsule.

I would still go ahead and archive off data if you need to .. then erase the TC and start over. That is the best way to get things back to starting point and running.

we have done all this and it still does not work - there is a bug somewhere

In the end Sierra did exactly what I told you to do..

Only I do hope you never need the old backups.. because deleting the existing backup is totally breaking the concept of a Time Machine backup.

i finally solved this issue by removing Sophos home internet security suite which also caused major issues with internet browsing, application speed and of course the time machine backups. I had to buy Carbon Copy Cloner to cover me during this period!

Is there any internet security suite that works correctly with MacOS??? Do we actually need a security suite ??????

Is there any internet security suite that works correctly with MacOS??

Not that I know of.. Sophos is probably as good as any but when the OS gets upgraded you need to wait for AV companies to get their act together.

Most of what AV product does in a Mac is prevent the spread of PC viruses. It doesn't actually protect the Mac.

Do we actually need a security suite ??????

If you use a Mac without PC in the environment I see no reason to run security suite. Apple have improved the security of the OS in latest versions and as long as you install all the security updates Apple send out.. and use smart internet practices.. plus good backup procedures I see no reason to worry. It doesn't mean you cannot be hacked but that it will be due to your own usage .. if you do things which are unsafe.. then use a computer that operates in a different vlan with a couple of bootable clones so you can immediately wipe the computer. Mostly the virus writers are still concentrating on windows world.

I had this problem and fixed it with an archive of the Airport Time Capsule to another disk, then erased it. I'm also using Bitdefender for Mac which is compatible with Time Machine and has additional Time Machine protection. I've not noticed any slow-down with Bitdefender - it's pretty light weight on the system. I used to use Sophos - but decided to do away with the free, slow and buggy software and just buy something good.

Hope that helps

btw - the issue I had:

Re: macOS Sierra Airport Time Capsule Time Machine backup is stuck in "Calculating time remaining..." after backing up 1GB of 60GB. No backups since macOS Sierra upgrade.

Cheers

Rik