Time Machine Not Backing Up

Noticed problem immediately after the last OS update

So was that Mojave?? How long ago was that?

since purchasing it in 2013

Does it happen to be the tall one or the flat model.. A1409 which is last N wireless? 2013 was the change over year.

Actually to get 6 years out of a Time Capsule (TC for short) is pretty good going and it really may well be due an update. Of course since Apple no longer make them you will need to figure out another alternative.

Have run disc first aid

This will not work on TC. It is a network drive. First aid in disk utility is only relevant to local disks.

Problems started in a major way at Sierra with enhanced security which Apple continues to do with each OS.

In Finder mount the TC disk.

Make sure you can see the sparse bundle for your computer.

If you have issues mounting the disk then Time Machine (TM for short) will have the same issue.

How much space do you have left on the TC drive?

This will show up in the Airport Utility on the disk tab.

Try using a verify by holding down the option key while you click the Time Machine icon.. it will show verify as an option.. if it is greyed out or doesn't work then next best step is to do a full factory reset of the TC and start over.

Power off the TC.. hold in reset button and power on again.. having another body to help makes it easier. You must not release the reset while you are powering on.. and keep holding it in for about 10sec. The front LED will start flashing rapidly.. if you missed it try again. Factory reset will not delete anything on the hard disk. It just removes settings on the TC which is necessary now and then.

Redo the setup of the TC from airport utility in your laptop. Do NOT use Apple recommended names.. start again with a new name which should be short, no spaces and pure alphanumerics. Password same rules but can be longer.

Once you complete the TC setup open the TM preferences and change the backup disk since it will have a new name and password. You might get a screen asking if this is to replace your current backup.. agree that it is replacement.

You will then see TM is going to do a full backup for the first time.. don't worry.. what happens is TM checks the disk for previous backups.. will find the existing backup.. verify it and continue if everything is good.

If it fails at that point the best thing to do is start over a fresh clean backup.

If you want to keep the old backup.. use the archive function you can see in the screenshot above to a USB disk (Mac OS HFS+ format) disk of equal size to the TC disk or larger. This will take several hours if it is large.. ie 1TB or more.

Then you can use the Erase function in the airport utility disk tab.. quick erase is fine.. to wipe the old backup and then you can start a fresh backup.

We don't know whether your Time Machine backup target is a Time Capsule, an external hard drive, or a NAS (Network Attached Storage) device.

You mention that you purchased a Time Machine at the same time as your Mac, but Time Machine is software on the Mac that used to back up the data on the Mac to another hard drive.

Perhaps you meant to say that you are backing up the Mac to a Time Capsule, which is hardware designed to handle Time Machine backups from your Mac. If that might be the case.......

Hold down the option key on your Mac while you click on the Time Machine "clock" icon at the top of the screen

Click on Verify Backups

Run the Verify Backups procedure, which may take anywhere from 5-60 minutes or more depending on how much data is stored on the Time Capsule disk.

If the verification process cannot run or cannot be completed, this unfortunately almost always indicates that your backup file has become corrupted, and will no longer be useable. In that case, the backup needs to be erased so you can start over again with a new backup.

Post back on your results.

Unfortunately, Time Machine backups to a network drive like the Time Capsule have been a lot less than reliable since High Sierra was introduced. Mojave continues to have the same type of corruption issues.

So, you will likely see the same issue appear again. The only real question in that regard is when......not if.

It might be a good idea to have a secondary backup plan in place with Time Machine backing up to a USB drive connected directly to your Mac. Cloning the drive with an application like Carbon Copy Cloner would also be a good idea. Good luck.

Tall rectangular TC ser#C02MN059FD59 ver 7.7.3

Your firmware is way out of date.. we are up to 7.9.1

Last back up was 8/17/19 ~15 min before taking my laptop to a friends house who has cable HS ISP (I have satellite) and downloading Security Update 2019-004. I brought the laptop back and almost immediately started to receive the error 21 message.

It is helpful to locate the actual point this started. As both Bob and I have commented .. Apple does a good job with security but it can have unfortunate side effects.

Hopefully the backup completes.. if not I would also think seriously about using CCC or another Mac backup software. TM has become too unreliable. I do run both.. CCC and TM.

About once every few months TM will destroy its own backup.

CCC has not let me down in a few years now.. and using it to a local USB drive as a bootable clone.. if something happens to the internal disk of the computer I can boot immediately from the external drive.