Time Machine: There isn't enough space - huh?

[Feek]

My iMac, MBA and Mac Studio all back up to a Time Machine partition on my Synology NAS. I know that it's getting low on space and I've just had this message.

But I thought that when the drive was full, Time Machine would manage it by deleting old backups.

I didn't think I'd ever see this message because of how TM backups work. There's nothing I should do to enable this deleting of old backups, is there? In all my years of Mac ownership, I've never seen this before.

Thanks.

 

[Bigwaff]

NAS TM backups are disk images. DMG grow but DMG not shrink. Your three backup DMG files have filled partition. Recommended you expand partition to double size needed for full backup of sources (3 Macs HDD space x 2)

 

[Feek]

The partition is already at least double the size of all three drives combined.

But each Mac is only using around 50% of the available drive space anyway. It’s just that over the years, backups have grown in size. Shouldn’t the oldest backups be removed from the sparebundles to make space for new ones?

 

[Ruggy]

Do you need to defrag it? If it's heavily fragmented then it can have plenty of free space but not enough contiguous space for a disk image. I haven't seen that problem for years though as they tend to handle that sort of thing so much better these days.

 

[Brian33]

Shouldn’t the oldest backups be removed from the sparebundles to make space for new ones?

Yes. Or at least TM used to work that way. In my past setup TM would remove the oldest backup(s) and compact the sparsebundle, which would make more space available on the backup volume. Worked with three different machines' sparsebundles on the backup volume. I'm not using TM much anymore, though, so I can't say about the newest versions of TM, but I think it's supposed to work the same way.

My guess is that you've hit a bug in TM. Perhaps the compacting of the sparsebundle is failing. It is possible to "manually" compact it using the 'hdiutil' command.

If you don't mind looking through lots of log messages, you could use the command below to see if any TM log message indicates what the problem is. Start the 'log' command in Terminal, start a TM backup, and the log messages will display in Terminal. Hit Ctrl-C to terminate the 'log' command.

log stream --info --style compact --predicate 'subsystem=="com.apple.TimeMachine"'

 

[HobeSoundDarryl]

I don't think TM always works well with multiple Macs sharing the same TM space. My guess is that one of them has eaten up the bulk of the available space for its backup and the new backup on another needs more space than the free space available. Yes, it should delete oldest files on its share of the space but maybe one of the Macs has- over time- eaten up so much space such that even with usual TM "oldest" deletions, there is not enough space for new backups of the specific Mac wanting to backup.

You might check to see how much of total space is "owned" by each Mac compared to how much total space you've allocated on that Synology. You might find that you have to delete the hog's TM backup, let the Mac trying to backup now do its backup in the (probably considerably) freed up space and then fresh backup the Mac backup you just deleted.

In other words, if total space you allocated on Synology was, say, 4TB, and one Mac has piled up enough history to "own" 3.6TB, the balance of only 400GB may not be enough for fresh backups for the other Mac trying to backup now. It's call for space probably can't deal with other Macs backup but only its own... and perhaps whatever it holds in that 400GB is not enough to reduce in the TM "oldest" files way to create sufficient space for updated files.

The analogy would be having a DAS drive attached on which you've added 3.6TB of other files and are trying to TM backup to only the 400GB that remains.

If you don't discover that one has gobbled up most of the space, you might have to wipe the whole TM space on Synology and then fresh backup each Mac again (basically start over with clean backups). However, if the above guess is right, you'll likely eventually fill up enough to get this problem again.

Another way to potentially address this is expand the allocation of space to TM on Synology to make the overall space larger. For example, if you've given it 4TB, expand it to 6TB to add 2TBs of fresh space to the overall pool. Then let the current Mac backup and that should work. I don't completely remember that adding space to Synology TM pool is possible without fresh backups after the expansion, but I believe it is. This should do the trick too.

 

[Bigwaff]

What version of DSM on Synology NAS? Does each Mac have its own shared folder for TM backups or are you using a single shared folder for TM backups? Are shared folder quota(s) set?

 

[Feek]

All Macs were reporting the error, it’s a single shared folder that they all access. No quota is set.

Each Mac backs up to two locations, the NAS and a local drive so I have history elsewhere. I deleted the two largest sparsebundles and they created new ones and off I go.