Size limit for shared network drive as Time Machine destination?

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Level 1

4 points

Size limit for shared network drive as Time Machine destination?

I have spent a lot of time researching this but it doesn't seem anyone has asked this before. So I'm trying now.

I have a M1 iMac and I had been using an external hard drive RAID directly attached as the main data drive, and an external hard drive JBOD of 44TB, also directly attached by USB, as Time Machine drive. It had been working fine for a couple of years.

I'm starting to run out of space on the main drive. While building a larger RAID as main drive, I'm also trying to relocate the TM drive to basement. I have another M1 Mac as well as an older High Sierra Mac that it can be plugged in as a network share.

I've spent a lot of time, trying different disk formats, and it basically works, but with one caveat that significantly reduces the value of this setup. That is I don't seem to be able to share a volume that's larger than 30TB for TM. On the client Mac after adding the remote drive for TM and starting the first backup, it would quickly fail with this message:

Time Machine couldn't complete the backup to "Backup HD".

The backup disk image could not be created.

The TM log shows these:

2023-10-17 09:38:30 Mountpoint '/Volumes/.timemachine/iMac M1._smb._tcp.local./D816C8EC-A3CF-470C-BCF3-BD9553B2A45A/Backup HD' is still valid

2023-10-17 09:38:30 Creating an unencrypted diskimage

2023-10-17 09:38:30 Mountpoint '/Volumes/.timemachine/iMac M1._smb._tcp.local./D816C8EC-A3CF-470C-BCF3-BD9553B2A45A/Backup HD' is still valid

2023-10-17 09:38:30 Using a band size of 9.77 GB on a volume sized 40.01 TB)

2023-10-17 09:38:31 Failed to create '/Volumes/.timemachine/iMac M1._smb._tcp.local./D816C8EC-A3CF-470C-BCF3-BD9553B2A45A/Backup HD/4BAD86CB-5EF0-51D4-988D-AC71D2BB4D70_2023-10-17-093830.sparsebundle', error: (null)

2023-10-17 09:38:31 Mountpoint '/Volumes/.timemachine/iMac M1._smb._tcp.local./D816C8EC-A3CF-470C-BCF3-BD9553B2A45A/Backup HD' is still valid

2023-10-17 09:38:31 Evaluating to see if an unmount was responsible for error: Error Domain=com.apple.backupd.ErrorDomain Code=20 "(null)" UserInfo={NSUnderlyingError=0x12103ce60 {Error Domain=com.apple.backupd.ErrorDomain Code=20 "(null)"}}

2023-10-17 09:38:31 Mountpoint '/Volumes/.timemachine/iMac M1._smb._tcp.local./D816C8EC-A3CF-470C-BCF3-BD9553B2A45A/Backup HD' is still valid

2023-10-17 09:38:31 Unmounted '/Volumes/.timemachine/iMac M1._smb._tcp.local./D816C8EC-A3CF-470C-BCF3-BD9553B2A45A/Backup HD'

2023-10-17 09:38:31 com.apple.TMHelperAgent.DeliverNotification: connection invalid

2023-10-17 09:38:31 Backup failed: BACKUP_FAILED_DISK_IMAGE_NOT_CREATED (20)2023-10-17 09:38:31 Analytics send failed.

After trying changing disk format and permissions, I eventually came to the conclusion it has something to do with the size of the network shared TM drive. If it's 30TB or below, it will work. Otherwise it won't. I switched between High Sierra and Sonoma Macs. The same result.

Can someone help?

Posted on Oct 17, 2023 6:50 AM

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Answer 1

engathome Author

Level 1

4 points

Nov 21, 2023 6:10 AM in response to engathome

For anyone who's reading this thread (especially you, Apple), I'm happy to report that Sonoma 14.1 seems to have fixed the issue. I didn't expect it after upgrading, but gave it a try anyway, and wa-la, the error didn't show up and it proceeded to backing up! I didn't downgrade to confirm but I'm relatively sure since I had tried many times before and a couple times after the upgrade.

But I'm facing another issue - it's actually an old issue because I had always seen it even when I had it working with <30TB TM drive - that the backup would stop at 16TB, claiming there is not enough space left. My TM drive has 68TB so obviously that's not an issue. I've tried this in various configurations for about 6 times - each took days to reach 16TB, my last try was 10 days!

I suspect this is another hidden MacOS limit that can be quickly removed if they wanted. I guess just not as many people have that much data to back up.

Please Apple!

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Answer 2

ku4hx

Level 7

23,694 points

Oct 17, 2023 7:00 AM in response to engathome

Help with what exactly?

If your internal drive is full, you'll need to free up space for TM to work properly. TM deposits its dataset on an external drive but it needs internal drive space to work.

Generally, the system drive needs 15-20% totally unused at all times to work efficiently. Sometimes that much to work at all for certain evolutions.

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Answer 3

engathome Author

Level 1

4 points

Oct 17, 2023 7:11 AM in response to ku4hx

Thanks for the quick response but I don't think you understood what I'm asking. My internal drive is fine. It has about 50% left. It was my main data drive that's an external RAID that's running low. But even that is beside the point.

What I'm asking is, if I use a network shared drive as TM destination, how can I configure it if it needs to be more than 30TB?

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Answer 4

engathome Author

Level 1

4 points

Oct 17, 2023 7:30 AM in response to engathome

Sorry folks if I wasn't clear in my original post. I realized I was babbling. Let me try again.

I'm trying to set up a network share as TM destination, using one of the Macs as the server. It basically works, but with what seems a limitation that the shared volume can not be more than 30TB in size. The error message and logs are in my original post.

I have tried APFS, APFS (case-sensitive), Mac OS Extended (Journaled) as disk format. They're all the same. I haven't seen anyone mentioned this limit so I'm hoping it's something I'm doing wrong. Thanks.

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