Time Machine can Overfill then Corrupt Backup Volume

[Cayenne1]

I have Time Machine backing up to two 1TB volumes. Eventually both drives will become full and TM normally deletes the oldest backup to make room.

However, I just had a case where TM failed to complete its task and MacOS errored out stating it could no longer write to that TM volume. But, MacOS stated it could "read" from that volume, and suggested the fix would be to copy all the TM files to another volume and reformat the errant volume.

A search showed that this TM issue is not uncommon and Disk First Aid will be useless. So heads up that Time Machine can overfill / corrupt its backup volume. You will then need to copy all the files from the TM volume to another volume "if available". Then reconnect TM to this new volume to retain its backup history. Otherwise, you must reformat the errant volume, connect it with Time Machine and only have backup as of that moment.

As a related FYI, never ever fill up any drive especially your system disk. MacOS cannot handle it.

 

[Apple_Robert]

A good general rule of thumb is to keep 20 - 30% of the internal SSD free, in order to keep the Mac working efficiently.

 

[ivanwi11iams]

To make sure I understand. The two 1TB volumes are on the same drive?

If yes, I remember about 6 months ago asking about this, on this forum, somewhere. I wanted to use my 2TB LaCie drive; 1TB for TM and the other 1TB for raw manual backups. I was told emphatically that it was a bad idea.

Looking forward to your response to my initial question. Thanks

 

[Cayenne1]

No, I have two 1TB volumes each on a separate 8TB external drive. There are no issues with any other volumes on either drive, i.e. no hardware or Disk First Aid errors. I've had this setup since 2019.

I also have two 1 TB Carbon Copy Cloner bootable volumes as well one on each of these drives. The remaining storage volume space is for data. I specify the multiple volumes in Time Machine. TM alternates every hour between the two volumes. I have two CCC tasks running after midnight to update the CCC backup volumes.

In essence, I have hourly (Time Machine) and daily (CCC) backups on two separate drives. In a way, Time Machine does monthlies as my oldest TM snapshot is Nov 2020. I recovered that snapshot because I use two TM drives. Otherwise I could recover files only to the last CCC daily last night.

I do use the cloud for Desktop and Documents as well, but prefer to keep my System HD lean as Apple_Robert mentions. Not perfect, but neither is Time Machine. Maybe Apple could invest some of their 1,000s of engineers in bullet proofing an app as mundane as BACKUP.

 

[NoBoMac]

A search showed that this TM issue is not uncommon and Disk First Aid will be useless.

Not uncommon, but also not common. Many people have been using TM with no issue, me included since day one. Where I've had issues is when the drive itself fails (which, yes, sounds like not OP issue here).

EDIT/ADD: where it seems like a number of TM issues come from are when NAS/RAID configurations come into play and might not play nicely vs simple external USB drive seems to generally do OK.

I wanted to use my 2TB LaCie drive; 1TB for TM and the other 1TB for raw manual backups. I was told emphatically that it was a bad idea.

Yes, bad idea in that if the drive fails, you have no backups. Does not follow a 3-2-1 like principal: 3 backups, 2 different media, 1 offsite. For home, if can't/won't do offsite, need a 2 and 2 backup (2 backups, 2 different media). Basically, more media, more better.

 

[PinkyMacGodess]

I recommended that people occasionally erase the drive, or have a second drive to use and swap them. It depends on what you might be able to live with as far as older backed up files being unrecoverable.

Creating a new epoch takes a lot of time with Time Machine. Wiping your only backup drive, and having the system fail in the process of doing essentially a full backup is living dangerously.

Regarding weird Time Machine moments, I had a TM drive that was 'unusable'. I tried to copy the files off of it, and got all the 'important files' and then tried to wipe it, and for some reason, couldn't. I ended up wiping it on a PC, and doing a low level on it, ran the factory diags, everything passed. Time Machine took the 'new' drive, and hasn't complained since. *shrug*