Time Machine says it cannot complete the backup because the disk is nearly full, but it is not. In fact, the Time Machine tab under System Preferences says "2.68 TB available".

Time Machine was working fine for a couple of years, then suddenly started getting this error. I have not made any major file or fold moves recently.

The external backup drive is 4TB G-DRIVE which has always been used exclusively for Time Machine backups. I noticed from the beginning that this single drive shows as two different mount points. Under "About This Mac / Storage", it shows as:

External 4 TB USB Disk

G-DRIVE mobile USB-C
2.86 TB available of 4TB

4.04 GB available of 4.08 GB

I assumed this was normal but perhaps it is not. If it's not correct, I don't know how to correct it.

G-UTILITIES just contains few instructional documents that came with the drive. They are about 30 MB total in size.

Under "About This Mac / Storage", my hard drive that I back up (Macintosh HD), shows "1.52 TB available of 2.12 TB". That is, it is about 71% full.

What do I need to do get the backups running again?

(I see other related posts on similar issues, but they are not quite the same. Most of them refer to Time Machine becoming confused by large file or folder moves which is not relevant in this case. And none of them address the 2 mount points for the single backup drive.)

Please see 4 screen shots below.


Time Machine error message

System Preferences / Time Machine tab show plenty of space

About This Mac show main hard drive and single backup drive with 2 mounts

Both drives as viewed from "finder" app.

@Jean_JD Okay "diskutil list" output is below followed by Time Machine options:

> diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *121.3 GB   disk0
   1:                        EFI ⁨EFI⁩                     209.7 MB   disk0s1
   2:                 Apple_APFS ⁨Container disk2⁩         121.1 GB   disk0s2

/dev/disk1 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *2.0 TB     disk1
   1:                        EFI ⁨EFI⁩                     209.7 MB   disk1s1
   2:                 Apple_APFS ⁨Container disk2⁩         2.0 TB     disk1s2

/dev/disk2 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +2.1 TB     disk2
                                 Physical Stores disk0s2, disk1s2
   1:                APFS Volume ⁨Macintosh HD - Data⁩     612.2 GB   disk2s1
   2:                APFS Volume ⁨Preboot⁩                 418.4 MB   disk2s2
   3:                APFS Volume ⁨Recovery⁩                611.0 MB   disk2s3
   4:                APFS Volume ⁨VM⁩                      3.2 GB     disk2s4
   5:                APFS Volume ⁨Macintosh HD⁩            15.1 GB    disk2s5
   6:              APFS Snapshot ⁨com.apple.os.update-...⁩ 15.1 GB    disk2s5s1

/dev/disk3 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *4.0 TB     disk3
   1:                        EFI ⁨EFI⁩                     209.7 MB   disk3s1
   2:                  Apple_HFS ⁨G-DRIVE mobile USB-C⁩    4.0 TB     disk3s2
                    (free space)                         135.2 MB   -
   3:       Microsoft Basic Data ⁨G-UTILITIES⁩             4.1 GB     disk3s3

/dev/disk4 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *2.0 TB     disk4
   1:                        EFI ⁨EFI⁩                     209.7 MB   disk4s1
   2:                  Apple_HFS ⁨DR Results⁩              2.0 TB     disk4s2

enter image description here

@Ezekiel: The tail of the script output is:

2021-06-04 14:08:30.515135-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:General] Starting automatic backup
2021-06-04 14:08:32.217070-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:General] Mountpoint '/Volumes/G-DRIVE mobile USB-C' is still valid
2021-06-04 14:08:32.220431-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:General] Mountpoint '/Volumes/G-DRIVE mobile USB-C' is still valid
2021-06-04 14:08:33.078935-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:General] Mountpoint '/Volumes/G-DRIVE mobile USB-C' is still valid
2021-06-04 14:08:33.079077-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:General] Backing up to G-DRIVE mobile USB-C (/dev/disk3s2,6): /Volumes/G-DRIVE mobile USB-C
2021-06-04 14:08:33.783037-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:Inheritance] Found matching machine store '/Volumes/G-DRIVE mobile USB-C/Backups.backupdb/K’s iMac' for computer named 'K’s iMac', no machine store inheritance needed
2021-06-04 14:10:38.181495-0600  localhost backupd-helper[288]: (TimeMachine) [com.apple.TimeMachine:PowerManagement] TMPowerState: 2
2021-06-04 14:10:38.182106-0600  localhost backupd-helper[288]: (TimeMachine) [com.apple.TimeMachine:General] Not starting scheduled Time Machine backup: Backup already running
2021-06-04 14:12:19.376008-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:General] Mountpoint '/Volumes/G-DRIVE mobile USB-C' is still valid
2021-06-04 14:12:21.408816-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:LocalThinning] Starting age based thinning of Time Machine local snapshots on disk '/System/Volumes/Data'
2021-06-04 14:12:21.408831-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:LocalThinning] Starting age based thinning of Time Machine local snapshots on disk '/System/Volumes/Update/mnt1'
2021-06-04 14:12:21.409116-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:General] Failed to wait for snapshot deletion to complete on disk '/System/Volumes/Update/mnt1', error: Error Domain=NSPOSIXErrorDomain Code=1 "Operation not permitted"
2021-06-04 14:12:21.409354-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:LocalThinning] Skipping age based thinning of Time Machine reference snapshot 'com.apple.TimeMachine.2021-05-26-120858.local' on disk '/System/Volumes/Data'
2021-06-04 14:12:22.250927-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:General] Failed to create APFS snapshot with name 'com.apple.TimeMachine.2021-06-04-141222.local' on volume '/System/Volumes/Data', error: Error Domain=NSPOSIXErrorDomain Code=28 "No space left on device" UserInfo={NSFilePath=/System/Volumes/Data, NSLocalizedDescription=/System/Volumes/Data: No space left on device (error 28)}
2021-06-04 14:12:22.251048-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:General] Failed to create local snapshots
2021-06-04 14:12:22.252183-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:General] Failed to create or mount stable snapshot.
2021-06-04 14:12:23.859850-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:General] Mountpoint '/Volumes/G-DRIVE mobile USB-C' is still valid
2021-06-04 14:12:23.860031-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:General] Mountpoint '/System/Volumes/Data' is still valid
2021-06-04 14:12:24.069831-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:General] Backup failed (50: BACKUP_FAILED_NO_SPACE_FOR_LOCAL_SNAPSHOT)
2021-06-04 14:15:07.075137-0600  localhost backupd-helper[288]: (TimeMachine) [com.apple.TimeMachine:PowerManagement] Thermal pressure level 0 -> 1
2021-06-04 14:15:07.078713-0600  localhost backupd[289]: (TimeMachine) [com.apple.TimeMachine:PowerManagement] Thermal pressure level 0 -> 1
Filtering the log data using "subsystem CONTAINS "com.apple.TimeMachine""
  • 2
    Can you add to your question the results of terminal command diskutil list and give the content of Options button in Time Machine preferences?
    – user415185
    Commented Jun 3, 2021 at 18:46
  • 2
    You can use this command to see more information: gist.github.com/ezfe/51725b2eae3e29e377d129aebe7cdc67
    – Ezekiel
    Commented Jun 3, 2021 at 18:52
  • 1
    It actually looks like your disk is nearly full. Do you have a FIFO setup for Time Machine in any case? Commented Jun 3, 2021 at 21:44
  • 1
    Your Time Machine partition is formated JHFS and now Big Sur use APFS for Time Machine. You can test format your TM disk in APFS an retry a backup. Be careful in this case, the previously saved data will be lost.
    – user415185
    Commented Jun 5, 2021 at 6:11
  • 2
    I have the exact same problem which also started a couple of days ago: "Time Machine could not back up the disk “Macintosh HD — Data” because it is nearly full." The problem is - that's a nonsense error message. According to disk utility: used->0.676TB while free->2.41TB The disk is only about 20% full. Even if it copied the whole thing to make a backup (onto a different drive which is blank/freshly erased and reformatted multiple times (including setting it back to Mac Extended Journalled to see if that made a difference)) and has 2TB free) there'd still be 60% free.
    – Rick
    Commented Jun 7, 2021 at 7:26

2 Answers 2


So I'm by no means an expert on Time Machine internals, but it's important to read error messages carefully and pay attention to grammar. (Apple, as opposed to Microsoft, is usually fairly careful to phrase their error messages precisely.) The error does not complain about the backup disk being full, but rather, about the disk to be backed up, i.e., Macintosh HD - Data⁩ being full. Looking at the log messages you posted shows why that is a problem: Apparently, TM tries to make a local snapshot first (presumably so that it can then make the backup without caring about changes to the live FS while backing up), but runs out of space while doing that: /System/Volumes/Data: No space left on device (error 28), Failed to create local snapshots, and Backup failed (50: BACKUP_FAILED_NO_SPACE_FOR_LOCAL_SNAPSHOT).

That's why it also tells you that you need to delete some files on this disk.

You can check with tmutil whether maybe you have a lot of existing local snapshots that you could thin out to make space, try tmutil listlocalsnapshots / and see if that lists previous snapshots or not. If it doesn't, I guess you'll really need to delete some stuff first (or at least move it elsewhere).

Hope this helps!

  • Yes, you're right about the importance of reading error messages carefully. However in this case Finder and other disk utilities were showing I had 1.46 TB of space available on my Macintosh HD. I wasn't aware of the distinction between "Macintosh HD" and "Macintosh HD -- Data". // The information about TM Snapshots is very useful. // The info about tmutil (Time Machine Utility) is useful. In all my research I had never seen mention of it. TM is such a complex utility, I had wondered why there wasn't such a utility. For anyone having TM issues I would suggest running "man tmutil". Commented Aug 5, 2021 at 15:19
  • 2
    Ever since the advent of Time Machine local snapshots, macOS gets very confused about the amount of space actually free: it tries to pretend that the space used by snapshots is actually free, but the truth tends to leak out…  The Finder, About This Mac, non-Apple apps, and low-level tools such as df can all have very different ideas about how much space is left.  (I got so fed up with unexpectedly running out of space when transferring big files that I set up a cron job to delete local snapshots every 5 mins!)
    – gidds
    Commented Aug 7, 2021 at 22:53
  • Frustrating indeed, because it says "Local snapshots as space permits," giving the impression that if there is no longer room for snapshots, things should continue to work as expected, and either new snapshots won't be created, or older ones will be removed making room for newer ones.
    – KevinHJ
    Commented Sep 21, 2022 at 12:24

I am happy to report this problem somehow cleared up by itself. I did nothing.

  • Lots of laughs... hard to replicate ;-)
    – Jon Kern
    Commented Dec 3, 2021 at 20:00
  • I had the same problem. Probably what KS did was just something that cleared whatever file was making the mac think it was "full" see the comments under the other answer. Commented Jan 30, 2023 at 13:03

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