Home Forums Mac Software Mac Operating Systems Time machine wants to start a first backup

I'm using Siera on a 2013 MB Pro. I have two external backup discs (hard drives) that I use with Time Machine.
I have just connected one of the backup discs and it seems to think that it hasn't been used before and wants to do a first back up on it.
In reality this disc has twelve previous backups on it and I want to add to these again.
The other disc is fine.
Any thoughts?

Time Machine can use the same drive to backup many different computers and users, but each will a separate backup set on that drive. For whatever reason it does not recognize the backup sets on that drive as being backups of your 2013 MB Pro and wants to create a new backup set for that computer.

What is your normal backup process? When do you do it? When do you use on drive or the other?

I generally use each disc once a month. It's a little random but I simply plug them in (USB) and press backup.
I have noticed that the icons of the backup discs on the desktop do change between orange to blue occasionally.
My main backup disc (4TB) is partitoned to work with my two machines, but the second discs are 1TB each and each works with just one of my MBP's. It's one of the these that isn't responding correctly, its icon is orange................ (I have double checked that I haven't attached the wrong one!)

As a double-check, open the Time Machine Preference in System Preferences. Click on "Select Disk…" and under "Backup Disks" you should see both of your drives listed. I alternate between two drives with my laptop and I see both of them when I do this. Select the drive you want and see if TM recognizes it and does not want to start new.

If you don't see your disk under "Backup Disks" or it tries to start fresh, then somehow it was forgotten or something is amiss with the disk. Try using an appropriate disk utility to check the disk for problems.

I have found that, if the TM disc becomes too full, it cannot be remedied (even by Disk Warrior). In that case (and I have done this about three times), I reformat the disk and start over. Yes, I lose all the data, but fortunately, it hasn't mattered.

For one reason or another the disk you have mounted is not being recognized as a Time Machine drive. The reasons include but are not limited to...

• The wrong drive is mounted
• The backup data set on that drive has become corrupted and is unrecognizable
• Changes in the MacBook Pro since the last backup on that drive are sufficient that it appears as if it were a different computer

Whatever the case your best options are either to create a second backup data set on the drive or if it were me I would simply erase the drive and start over from scratch with a clean new backup dataset. (I have been able to convince Time Machine to adopt an existing backup data set, but that occurred in the context of upgrading to a new computer and I have been unsuccessful in triggering that adoption otherwise. 🤬)

OPINION: Time Machine is ill suited to your backup pattern. It is intended to enable restoration of individual files or even the entire system from hourly points in time and does so by creating hourly backups for the past 24 hours, daily backups for the past month, and weekly backups for all previous months. (The oldest backups are deleted when your backup disk is full.) The way you are using it loses ~90% of its functionality. Given your backup pattern Carbon Copy Cloner or a similar utility would seem to be a superior fit and could even result bootable backup volumes. (Time Machine backups are NOT bootable.)

Thanks for all of your thoughts and suggestions. I appreciate your time.
I'm happy to start over with the disk and will consider using different backup software.
Thanks again.

Disk gets full......have to start again. That's my experience and it really ticks me off. I have always set TM to drop the oldest files in order to make room for new ones, but it has yet to work that way.

The fact you are running out of Time Machine disk space is an indication your Time Machine drive may not be properly sized for your system.

I have a single backup data set that is four years old and on its third computer. I followed Apple's recommendation the Time Machine drive should be 3 to 4 times the size of the drive(s) being backed up so it is a 3TB RAID 5 array that started out backing up a 1.2TB Fusion drive and continues to backup 1.5TB of SSDs today. Given that I choose to backup the system files as well as users files and as a beta tester go through a system update roughly ever three weeks and with all that there are still 826GB available on the 3TB array!

To be fair the life of the RAID backup has been extended somewhat, because about a year ago I added a second Time Machine drive so TM alternates between the two drives hourly but there is a full backup set for the past year on both drives. That second backup set is now up to 581GB.

My point is TM is amazingly efficient in the use of drive space and with a properly sized drive, it should take a LONG time to overflow.