Sparsebundle file vs. dated Time Machine backup files

I am now trying to do the Verify ... when I initiate that by clicking on Verify while holding down the Option key, it seems to start, but no window pops up and nothing happens. How will I know if the verify is successful?

The instructions that I posted previously above mention that you can watch the progress of the Verify Backups check by clicking on the Time Machine "clock" icon and then opening Time Machine Preferences. The window looks very similar to the window that you see if you are running a regular backup.

A message on the screen should appear when the check is complete or the process encounters a problem in which case an error message will appear on the screen. Note the exact text of the message if this occurs please.

but have seen reports of Time Machine backups becoming corrupted.

We see reports about this all the time over in the Time Capsule support forum. The issues have really increased since the intro of Big Sur and Monterey. In the case of the Time Capsule as a network drive, that disk can only be formatted as Mac OS Extended (Journaled), so Time Machine tries to set up the sparsebundle backup as APFS (Case sensitive). So, you have an APFS formatted sparsebundle backup on a disk that is formatted differently.

In theory, things should work. In practice......on the now 8+ year old Time Capsule design......I'm not so sure how well the theory holds up, since the Time Capsule was engineered long before APFS appeared and Apple never changed the hardware or offered any updates other than security.

Check the format on your external drive. Time Machine auto formats my externals as APFS (Case Sensitive), even if the drive is originally formatted as HFS+ or APFS. Example:

For what it's worth, the documentation on my Synology NAS states clearly that the drive must be formatted HFS+ for use with Time Machine.

The difference between the formats is forced. Backing up to a network drive needs to use a sparsebundle (a disk image) and the TimeMachine file structure is inside the container file.

There's not really enough information in your post to identify what the problem might be. Are any files being backed up at all? (have you tried to restore a file at random to see if it is in the backup?)

If Time Machine is backing up to a network drive, the target disk must be formatted in Mac OS Extended (Journaled), aka HFS+.

The hard drive on Big Sur and Monterey Macs is formatted in APFS. If you are trying to back up the Mac(s) to a network drive, Time Machine has to try to copy data from an APFS disk (your Mac) to the backup disk which is formatted completely differently.

Gosh, I wonder what could go wrong with this extra complexity? It's much easier for the Time Machine backup to become corrupted.

To see if that might be the case with your Time Machine backups to a network drive.......

Hold down the option key on your Mac while you click on the Time Machine "clock" icon at the top of the Mac's screen

Select Verify Backups and run the check

The check might take anywhere from a few minutes to an hour or more depending on how much data is stored in the Time Machine backups. Let the process run until it completes or until you see an error message.

If an error message appears, please post back with the exact text of the message.

You can watch the progress of the check by clicking on the Time Machine "clock" icon again and the clicking on Open Time Machine Preferences

I'd assumed that the backup to your Drobo for the problem machine had never worked but realise now that this is not the case. I don't know what this might have happened, but have seen reports of Time Machine backups becoming corrupted. The no space error may just be a result of that.

Certainly if there is no quota set for the share nor a maximum size set for the sparsebundle, it should just grow until it takes up all the space on the disk. When a backup starts, the "Preparing" phase includes a check of available space and if there isn't enough space for the new backup, Time Machine removes the oldest backup in this phase so if there really were not enough space, the error should happen during the Preparing phase.

You do need to have the Time Machine Preferences window open when you start to use Verify to be able to see anything. It doesn't open a dedicated window but displays the status in the Preferences pane as it searches for the drive, then goes into a state of preparing to verify, then "Verifying backup..." with a progress bar. This can take a (very) long time. When it finishes the progress bar disappears but as far as I'm aware there's no confirmation of success. I assume there probably would be something if verfication failed but I can't say for sure as I've never seen an error. I may just be lucky but I've been backing up 3 Macs to a NAS (not a Drobo though) for about 3 years now and not had any problems other than the occassional error completing a single backup (with success when it runs an hour later).

I set up the external just a few days ago.....formatted as APFS. Time Machine changed that automatically to APFS (Case Sensitive)

Sorry, I didn't make that clear. Yes, it formats the drive APFS (Case Sensitive). There is nothing you can do about that.

It doesn't back up the way it used to under HFS+ (though it will continue an HFS backup). It has to be APFS since it makes a snapshot, then copies the snapshot and integrates it with the other snapshots. All of that should be faster and more efficient.

My direct-connect drive actually has two Time Machine Volumes, one for the Mini and one for a network drive.

You have to set up multiple Time Machine volumes in Terminal as the GUI doesn't do it correctly (but, I haven't checked in a while).

The file system is a red herring. The OP is asking about backing up to a network drive. That will not be any of the flavours of APFS which is why the sparse bundle is created. Sparse bundles are effectively disk images and the necessary formatting for Time Machine is done within it.

It sounds like you now have it working.

It doesn’t matter what format the NAS chooses. Time Machine will create a sparse bundle disk image that is APFS. (Case sensitive).

Time Machine on Monterey uses APFS (case sensitive) as it manipulates APFS snapshots instead of the previous scheme. When you set up a new backup in Monterey, it formats the drive that way. As you noted in the question, the backup appears as a bunch of dated folders. There aren’t any parent folders because you can only back up a single Mac to a single APFS volume.

If verification completed successfully, then that is a very good sign. The verification process tries to correct errors as it goes, similar to First Aid in Disk Utility. So, the minor file system errors may have been corrected.

Would be interested in learning about the results of the Drobo check if you have the time.

If Time Machine is backing up to a network drive, the target disk must be formatted in Mac OS Extended (Journaled), aka HFS+.

That is completely wrong. A network backup creates a Sparse Bundle Disk Image of the correct file system on whatever file system is hosted by the network storage device.

Please explain why I cannot back up using Time Machine to any of my network drives unless the drives are formatted in HFS+. Two trips to the Genius Bar at two different Apple Stores say the same thing.

Yes, the sparsebundle file itself on the HFS+ formatted network drive might be formatted APFS (Case sensitive), but that is not what I am asking about.

If I try formatting the network drive in APFS or APFS (Case sensitive) no way will the backup run. What's the secret if you know?

Sure, backups run fine to a local drive formatted as APFS (Case sensitive) which is connected directly to the Mac.

Bob Timmons wrote:

Please explain why I cannot back up using Time Machine to any of my network drives unless the drives are formatted in HFS+.

No idea. My two network backup drives on my M1 Mini are APFS.

Now, it probably needs to be a modern file system, so any FAT may not work. NTFS, NFS, EXT4 will all likely work.

A direct connected drive will be formatted APFS by Monterey.

The Mac sending files to the network storage has no care about the file system on the destination as it doesn't write anything to the storage. The host computer writes data to the storage device.

My direct-connect Time Machine drive that backs up the M1 Mini is APFS, but we're not talking about those.

The topic of the post is Network storage devices.

The two drives I use to back up my other Macs are both APFS.

Understand, but wonder why we are both getting different results on externals.

I set up the external just a few days ago.....formatted as APFS. Time Machine changed that automatically to APFS (Case Sensitive)