Difficulty inheriting Time Machine backups via old MacBook Pro set up to be a wireless server for USB backup drive

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Difficulty inheriting Time Machine backups via old MacBook Pro set up to be a wireless server for USB backup drive

I'm having difficulty getting a Time Machine backup external drive to now function via a old MacBook Pro I'm setting up as wireless server. Goal: to be able to wirelessly do Time Machine backup from the 2 others MacBook Pros we use.

Details of former setup:

Sandisk 8TB GDrive was being manually connected by USB-C cable to one of our MacBook Pros and then the other, to do Time Machine backups, about 1x a week. Also had all files being backed up on Google Drive. The GDrive is set up with 2 partitions for the respective Time Machine backups, both 1.5 TB APFS formatted, plus a 5TB partition for other general storage, formatted MacOS Extended (Journaled).
My wife's MBP - now replaced with a newer one - is what I'm now using at a wireless server. It is an early 2015, running Monterey 12.7.6 - completely wiped and set up fresh - I was thinking of selling it.
My MBP - also replaced now - was a mid-2017 running Ventura (13).
Both of these were doing fine with their Time Machine Backups

Current attempted setup:

Backup drive: same Sandisk 8TB GDrive with same partitions, connected by hi-speed USB cable to the server.
Server: early 2015 MBP running Monterey 12.7.6, and connected to router by ethernet cable via thunderbolt adaptor. Has a main account and a 2nd (if needed for emergency) administrator account
- Sharing: File Sharing is on; All three partitions from the GDrive are listed as shared folders; All three have read...write selected for main user, staff, and for everyone. Under options, both main & 2nd accounts have SMB sharing enabled - not sure that was needed, but trying it anyway.
- Also have Remote Management sharing turned on.
My new-to-me MBP is a 2020, running Tahoe 26.2. My wife's new MBP is also running Tahoe 26.2. We did inherit the Time Machine backups to our new MBPs by manually attaching to the GDrive via USB, and so that is working - but still terribly inconvenient.
On my MBP, in the Time Machine window, I can see my Backup (which I can use by manually connecting via USB to the GDrive).
When I hit the + button to add a drive (I think this is the correct path), I still get this message: "The selected network backup disk does not allow reading, writing and appending. Please connect as a different user ... "

So I'm stuck. Help! Any wisdom about what I should do to get these backups working again remotely via the server?

Thanks!

MacBook Pro 13″, macOS 26.2

Posted on Dec 23, 2025 11:06 AM

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Answer 1

Top-ranking reply

Grant Bennet-Alder

Level 10

140,771 points

Dec 27, 2025 6:25 PM in response to JerryGP

When you use a Server (any Server, including NAS or another Mac) as a Shared Time Machine Backup Destination, the process launders out the minutia of the Server Drive format by creating the backup SET inside a sparse bundle disk image. That is an expandable DRIVE inside a single file on the server.

You will not be able to easily inherit an old backup set and have it continue its life as a Server-based Time Machine Backup Destination. The existing backup set was not created inside a sparse bundle disk image file.

My suggestion: Pull together some old external drives and create one local backup for each Mac today. that way you are never "working without a net".

Then start over on the Big server drive, erasing the old backups and creating one big partition. Use the official method to create Shared Time Machine Backup Destinations on the Server drive. Each shared destination can be species as a maximum size as it is set up.

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Answer 2

Dec 31, 2025 11:14 AM in response to JerryGP

Rather than shrink those partitions and keep them on an active drive,

My suggestion: Pull together some old external drives and create one local backup for each Mac today. That way you are never "working without a net".

Then start over on the Big server drive, erasing the old backups and creating one big partition. Use the official method to create Shared Time Machine Backup Destinations on the Server drive. Each shared destination can be species as a maximum size as it is set up.

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Answer 3

Dec 27, 2025 7:21 PM in response to Grant Bennet-Alder

The late James Pond wrote a wonderful linked set of illustrated tutorials and explainers for Time Machine. it is still applicable today, and a mirrored article regarding sparse bundles is here;

How Time Machine Works its Magic: How Network Backups are Stored in Sparse Bundles

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Answer 4

JerryGP Author

Level 1

7 points

Dec 31, 2025 6:27 AM in response to Bigwaff

Hi, Bigwaff,

I will have to stop using the current Time Machine backups which are each taking a fraction of their 1.5 TB partitions. So they won't be growing. I don't want to discard them, because they contain several years of history of files I might want to retrieve. I think I'm going to shrink those 2 partitions to barely contain those backups, and then start new network backups on a different part of the remaining drive.

thanks! - JerryGP

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Answer 5

JerryGP Author

Level 1

7 points

Dec 31, 2025 6:22 AM in response to Grant Bennet-Alder

Yes, thanks, I remember seeing the sparsebundles when we had one of the old Time Capsules as a networked backup drive.

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Answer 6

Bigwaff

Level 1

65 points

Dec 23, 2025 1:28 PM in response to JerryGP

You can't convert a local disk TM destination to a network TM destination in the way you are attempting. Local and network are two very different TM destination types. Some years ago I tried this -

https://ericfromcanada.github.io/output/2021/migrating-time-machine-backups-to-network.html

without success. YMMV. In the end, I decided to start clean w/ network TM destinations. Good luck.

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Answer 7

JerryGP Author

Level 1

7 points

Dec 23, 2025 1:52 PM in response to Bigwaff

Ok, thanks Bigwaff for the info. Not what I wished to hear, but definitive.

So... I'm wondering how to keep the current TM backups (which CAN be accessed manually), and recover the unused space from each of the 1.5TB partitions they currently occupy; and then I suppose set up new partitions on that same drive. Any wisdom there?

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Answer 8

Bigwaff

Level 1

65 points

Dec 27, 2025 5:37 PM in response to JerryGP

JerryGP wrote:

Ok, thanks Bigwaff for the info. Not what I wished to hear, but definitive.

So... I'm wondering how to keep the current TM backups (which CAN be accessed manually), and recover the unused space from each of the 1.5TB partitions they currently occupy; and then I suppose set up new partitions on that same drive. Any wisdom there?

If I follow the thread, you have 8TB drive which has 3 partitions, 2x 1.5TB each used as Time Machine backup for both you and your wife's Macs, and a 5TB HFS+ partition for other purposes. What unused free space are you referring to? Don't you want your 1.5TB TM partitions to have room for backups to grow?

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Answer 9

Dec 23, 2025 11:09 AM in response to JerryGP

First off, did you follow the instructions here to stand up the old Mac as. TM server?

Back up to a shared folder with Time Machine on Mac - Apple Support

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Answer 10

JerryGP Author

Level 1

7 points

Dec 23, 2025 11:15 AM in response to neuroanatomist

yes, I did. all as that recommends. I see that it DOES say turn on the SMB; yes they are shared as time machine backup destinations. thanks for the reply

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