HT201250 Backup too large & time machine not backed up for over a year.

Today I got this message:
This backup is too large for the backup disk. The backup requires 188.89 GB but only 73.07 GB are available.
Time Machine needs work space on the backup disk, in addition to the space required to store backups. Open Time Machine preferences to select a larger backup disk or make the backup smaller by excluding files.
Then when I go to preferences it said
73.1 GB of 320 GB available
Oldest backup July 10, 2011
Latest backup July 10, 2011
Next back up Today at 7:25pm
I was under the impression I had been backing up everyday and today was the first day I go the warning the backup was too large. Why is it that I have not had a back up for over a year? That worries me. I had a HD crash just over a year ago and the time machine saved my life. I thought everything was back to normal once I had my new HD installed, but wondering if that was the last back up it ever did for some reason.
Any suggestions? I am going out to get a new external HD of 1TB and hoping all will start backing up again.

Hi, what Mac Utilities is this you ran?
Have you looked through Pondini's extensive TM help site?
http://Pondini.org/TM/FAQ.html
http://pondini.org/TM/Troubleshooting.html
Can't imaging something not being covered there.

Similar Messages

Time Machine not backing up

Why is my Time Machine not backing up my documents, folders and files.
I have a Mac oss 10.5.4. 2 GHz Intel Core Duo, 1.5 GB. I have been trying to remove files as I'm running all my programs slow. I recently installed the recent ILife upgrade.
Often I would go in and turn off the hourly time machine backup because as I was working on memory intensive programs such as Photoshop I found it may have been linked to crashes. This is particularly concerning as the backups aren't accessible anyway.
Okay, this is the stupid part - on my part - I included my (House) folder in the files not to back up. I was mistaken as to this being a way not to have redundant back ups.
However; the only file now that is in the do not back up is the (time machine backups) and still nothing is saving - particularly concerning? iphoto file. see below.
Now this is concerning! I restored all photos from "March 13, 2008" - it's september. to IPHOTO from Time Machine. I don't know what changed since then(?) I thought it would add these folders into my i photo cache. This of course has involved a software upgrade since to iphoto. I was prompted for upgrade to the restore. So I said yes, to assure the photos added? where in a compatible format. However; instead it has erased all my photos SINCE. Are my photos irretrievably lost?
Why won't my files back-up for retrieval? Can I restore my settings from March 13, 2008 when my Time Machine back-up worked?
I find it horribly confusing that I no longer can access the photo cache, instead having the 'iphoto cache' icon.
This feels like PC headache. I am about to give up!

One thing you can check (using disk utility info button) is that the disk used for backing up must be in the Mac OS Extended (Journaled) format, and must have Access Control Lists enabled. Permissions must be set so that you are allowed to use the disk, and the disk can’t be read-only. There must also be sufficient room on external disk for the entire TM backup. Since apple recommends just using TM on the disk, one thing to contemplate if having problems you can't resolve is to reformat as the above and start from scratch.

Time Machine not backing up. Very slow, essentially hanging. I have 10.7.5 Mac OS X Lion (11G63). I have put in all updates. I tried to put my folders into "private" in the Spotlight (b/c I read that might be the problem). Still not working.

Time Machine not backing up. Very slow, essentially hanging. I have 10.7.5 Mac OS X Lion (11G63). I have put in all updates. I tried to put my folders into "private" in the Spotlight (b/c I read that might be the problem). Still not working.
Thanks in advance for any help!

For all things Time Machine see Pondini's excellent information here...
http://pondini.org/OSX/Home.html
Start at Troubleshooting.

Time Machine not backing up music added to iTunes since the original backup

My girlfriend has a Macbook and I decided it was time for her to back up. I used Time Machine with my Lacie external HD. The original back up got all the music, documents, etc.
This morning was the first time I had hooked up the external HD since the original back up. I manually ran it and wanted to check if it added the new music and documents. My resume, which I updated last night, was there. But when I looked in the iTunes folder the new music I had added was missing.
Will the daily or weekly back up get the new music files? Is there something I did wrong with set up? Of course I could start over but I'd rather fix the issue and make sure everything is being backed up.
Your suggestions or comments are appreciated.

Erik Griffin wrote:
My girlfriend has a Macbook and I decided it was time for her to back up. I used Time Machine with my Lacie external HD. The original back up got all the music, documents, etc.
How long ago was this?
This morning was the first time I had hooked up the external HD since the original back up. I manually ran it and wanted to check if it added the new music and documents. My resume, which I updated last night, was there. But when I looked in the iTunes folder the new music I had added was missing.
How are you verifying whether they were backed-up? Use +Enter Time Machine,+ not the Finder.
Will the daily or weekly back up get the new music files?
The labels of hourly, daily, and weekly backups are just labels. The process is the same with each. The only thing that's different is how long TM will keep them. A TM backup is a TM Backup.
Is there something I did wrong with set up? Of course I could start over but I'd rather fix the issue and make sure everything is being backed up.
First, check TM Preferences > Options. Be sure nothing is listed there that would prevent any iTunes data from being backed-up.
If you still don't see them, download the TimeTracker app, from www.charlessoft.com.
It shows most of the files saved by TM for each backup (excluding some hidden/system files, etc.). That should show what was actually backed-up.

Time machine not backing up user home directories

Hi All,
I set up my users to have their home directories on a seperate partition: /Volumes/Data/homes/<name>.
I confogured time machine to back up to an external USB hard drive. The exclude list is empty, exept for the backup disk, of course.
When i do an initial backup with TM, i notice that /Volumes/Data/homes is skipped, whereas /Volumes/Data/kits is backed up.
I also see a console message:
8/15/13 3:21:29 PM
com.apple.backupd[621]
Backup content size: 119.8 GB excluded items size: 113.6 GB for volume Data
Why is this? How can i force TM to backup all files?
Thanks for your help,
Heinrich

HeinrichFromBremen wrote:
Of course not. But there is a difference between lack of perfection and deliberately building bugs into the software.
It's not really deliberate. The number of folks who do what you are is very, very limited.
How can i know that homeis the only omitted directory?
It isn't. As noted in the other thread, dev and net are also omitted. Many other things, are, too - see the tan box in Time Machine - Frequently Asked Question #11 for details.
With this behaviour, i simply cannot trust TM backups.
A bit of an overreaction, I think, but your choice.
What would be the alternatives? tar? ditto? dump does not seem to exist.
See #27 in the FAQ link above. As far as I know, they all omit some things.

Time Machine not backing up anymore

I'm using TimeMachine for my wireless internet as well as for backing up my hard drive. The internet works fine.
The issue that I am having is that Time Machine is no longer backing up my hard drive. The last backup was in November. Up until that time, I had backups daily. The only thing I can think of is that Time Machine is no longer deleting the oldest backup to make room. I tried to go in and delete the oldest backup, but after like 10 hours, it still hasn't deleted.
Any suggestions?

nago_uchinanchu wrote:
The only thing I can think of is that Time Machine is no longer deleting the oldest backup to make room. I tried to go in and delete the oldest backup, but after like 10 hours, it still hasn't deleted.
How did you do that? If you used the Finder, your backups are corrupted.
How large is your Time Capsule's HD, and how much data is on your system? Since there hasn't been a backup in months, Time Machine will probably try to do a full backup. Your best bet may be to connect via Ethernet if at all possible, erase the TC's hard drive (use +*Airport Utility.+* Select +*Base Station > Manual Set-Up+* from the Menubar, then Disks in the tool Bar, then Erase.) Then let Time Machine start fresh.
Otherwise, try a +Back Up Now+ (from the TM icon in your Menubar, or by right-clicking the TM icon in your Dock) and see what happens. If you get an error message, start with the Time Machine - Troubleshooting *User Tip,* also at the top of the +Time Machine+ forum. It will show you how to locate the message(s) that describe the problem, then help you fix it.
If that doesn't help, post back with details, including all the messages, your setup, what you've done, and the results.

Time Machine not backing up 2nd external drive, remove option grayed out

I have two external hard drives, 300gb (firewire) and 500gb (usb). Time Machine is backing up to the 300gb. In Time Machine's options, the 500gb is excluded from being backed up, and the remove option is grayed out.
The 300gb Time Machine Backup drive is formatted as Mac OS Extended. The 500gb drive is formatted as MS-DOS (FAT32).
I know the backup drive needs to be formatted as Mac OS Extended, but will it not even back up other drives that are FAT32?

I am having a similar problem. I initially set it up 3 days ago and had it back up just the iMac to Time Capsule (about 120 GB) which it did no problem (I initially had my LaCie drive excluded). I then un-excluded my other drive, where all my photos and music reside (about 130 GB). Since then, it keeps trying to back up about 102 GB each time. Looking at the list of backups it does not appear that it has ever successfully backed up the LaCie. I am not aware of any error messages, but I have not been home much. I normally shut down the computer at night but I have been leaving it on trying to let Time Machine do its thing. All I can say is that every time I am at the computer TM is running and it always looks like it is in the middle of backing up 102 GB (usually seems to be near the beginning, never seem to see it more than halfway done). Looking at the TM panel it says the latest backup was 2 days ago. I'd appreciate any advice!

Time machine not backing up new changes

Time machine was working perfectly fine until this past weekend. Now, it seems like it's not recognizing any new changed on my hard drive. The time machine still runs successfully, but it just repeats the same back up over and over again. I've checked the logs in console (see below)
Dec 15 00:35:25 localhost com.apple.backupd[6749]: Starting standard backup
Dec 15 00:35:25 localhost com.apple.backupd[6749]: Backing up to: /Volumes/Time Machine/Backups.backupdb
Dec 15 00:35:33 localhost com.apple.backupd[6749]: No pre-backup thinning needed: 424.6 MB requested (including padding), 281.50 GB available
Dec 15 00:35:34 localhost com.apple.backupd[6749]: Copied 5 files (33 bytes) from volume Macintosh HD.
Dec 15 00:35:34 localhost com.apple.backupd[6749]: Starting post-backup thinning
Dec 15 00:35:34 localhost com.apple.backupd[6749]: Deleted backup /Volumes/Time Machine/Backups.backupdb/Adrian Ma’s MacBook Pro/2009-12-13-233455: 281.50 GB now available
Dec 15 00:35:34 localhost com.apple.backupd[6749]: Post-back up thinning complete: 1 expired backups removed
Dec 15 00:35:34 localhost com.apple.backupd[6749]: Backup completed successfully.
I've also downloaded Time Tracker and it says that things were fine till this weekend and then everything for the past couple of days have 0 bytes backed up. Any ideas what could be the problem? I haven't done anything special or changed anything besides install Google Chrome. The external hard drive I back up to may have been unplugged/plugged but not before it's unmounted or the computer is off. I don't think I unmounted while time machine was backing up, but if I did could this be the problem?

ecanza wrote:
Solved! Thanks for the swift replies! I didn't do a Verify Disk, but I did do a Verify Disk Permissions without restarting recently.
Are you sure? Because +Verify Permissions+ doesn't do it. Only +*Verify Disk,+* or altering any partition on your boot drive.
There are some 3rd-party disk repair/maintenance apps that use the same internal OSX routine as +*Repair Disk,+* so if you used one of them, you'd have the same problem.
And by the way, there's no point to running +Verify Permissions+ -- you might as well just run +Repair Permissions.+
I just restarted and Time Machine has in fact "caught up" with the most recent changes! Cheers Pondini.
Oh, well, whatever it was, I'm glad it's fixed! And thanks for the star.

Time Machine Not Backing Up New Files

Time Machine is NOT backing up my recent files.
I recently noticed that Time Machine was backing up really quickly instead of taking several minutes as usual. I checked previous backups and discovered that NONE of my recent files were backed up.
I have a very basic setup. An external usb 1 tb drive formatted as Mac OS Extended (Journaled) being used as the time machine backup drive. A new i5 mac mini with OS X 10.8.4. About 200 gigs of data with one user on the internal drive.
I have followed all of the Pondini troubleshooting steps. I have restarted into safe mode to force a deep traversal. I have repaired permissions and verified all disks with Disk Utility. I have deleted time machine preferences and followed instructions as per Pondini #A4. The backup seems to run but then finishes quickly but DOES NOT BACK UP any recent files.
I have run TMUTIL COMPARE, it showed that many files needed to be backed up.
I have run TMUTIL ISEXCLUDED on some of the files that were not being backed up. It showed that they were not flagged for exclusion.
I have run a manual backup after starting up in Safe Mode, which forced a deep event scan, but then exhibited the same behaviour..
I have acquired a new external hard drive, backed up the complete main drive (using Time Machine which appeared to be successful on the first time full backup), then run a manual backup on that new drive after adding new files and had THE SAME PROBLEM.
Here's the latest console output, which is typical since I have noticed this issue. There appear to be many megabytes of new files to be backed up, but then the operation completes within seconds and no files are backed up at all.
6/23/13 7:15:16.422 AM com.apple.backupd[643]: Starting manual backup
6/23/13 7:15:16.966 AM com.apple.backupd[643]: Backing up to: /Volumes/Omnius/Backups.backupdb
6/23/13 7:15:17.916 AM com.apple.backupd[643]: Using file event preflight for Olympus
6/23/13 7:15:20.277 AM com.apple.backupd[643]: Will copy (375.1 MB) from Olympus
6/23/13 7:15:20.298 AM com.apple.backupd[643]: Found 845 files (375.1 MB) needing backup
6/23/13 7:15:20.311 AM com.apple.backupd[643]: 1.91 GB required (including padding), 747.18 GB available
6/23/13 7:15:29.264 AM com.apple.backupd[643]: Copied 400 files (1.4 MB) from volume Olympus.
6/23/13 7:15:29.298 AM com.apple.backupd[643]: Using file event preflight for Olympus
6/23/13 7:15:29.299 AM com.apple.backupd[643]: Will copy (Zero KB) from Olympus
6/23/13 7:15:29.300 AM com.apple.backupd[643]: Found 5 files (Zero KB) needing backup
6/23/13 7:15:29.301 AM com.apple.backupd[643]: 1.46 GB required (including padding), 747.17 GB available
6/23/13 7:15:30.439 AM com.apple.backupd[643]: Copied 140 files (33 bytes) from volume Olympus.
6/23/13 7:15:30.511 AM com.apple.backupd[643]: Created new backup: 2013-06-23-071530
6/23/13 7:15:30.608 AM com.apple.backupd[643]: Starting post-backup thinning
6/23/13 7:15:30.608 AM com.apple.backupd[643]: No post-back up thinning needed: no expired backups exist
6/23/13 7:15:30.689 AM com.apple.backupd[643]: Backup completed successfully.
Please help. Time Machine is currently useless as a backup solution.

Results (username obfuscated in exclusionpaths):
   -=-=-=-=-=--
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
          <key>sourcePaths</key>
          <array>
                    <string>/</string>
          </array>
          <key>standardExclusionPaths</key>
          <array>
                    <string>/.MobileBackups</string>
                    <string>/MobileBackups.trash</string>
                    <string>/.MobileBackups.trash</string>
                    <string>/.Spotlight-V100</string>
                    <string>/.TemporaryItems</string>
                    <string>/.Trashes</string>
                    <string>/.com.apple.backupd.mvlist.plist</string>
                    <string>/.fseventsd</string>
                    <string>/.hotfiles.btree</string>
                    <string>/Backups.backupdb</string>
                    <string>/Desktop DB</string>
                    <string>/Desktop DF</string>
                    <string>/Network/Servers</string>
                    <string>/Library/Updates</string>
                    <string>/Previous Systems</string>
                    <string>/Users/Shared/SC Info</string>
                    <string>/Users/Guest</string>
                    <string>/dev</string>
                    <string>/home</string>
                    <string>/net</string>
                    <string>/private/var/db/com.apple.backupd.backupVerification</string>
                    <string>/private/var/db/efw_cache</string>
                    <string>/private/var/db/Spotlight</string>
                    <string>/private/var/db/Spotlight-V100</string>
                    <string>/private/var/lib/postfix/greylist.db</string>
                    <string>/Volumes</string>
                    <string>/Network</string>
                    <string>/automount</string>
                    <string>/.vol</string>
                    <string>/tmp</string>
                    <string>/cores</string>
                    <string>/private/tmp</string>
                    <string>/private/Network</string>
                    <string>/private/tftpboot</string>
                    <string>/private/var/automount</string>
                    <string>/private/var/folders</string>
                    <string>/private/var/run</string>
                    <string>/private/var/tmp</string>
                    <string>/private/var/vm</string>
                    <string>/private/var/db/dhcpclient</string>
                    <string>/private/var/db/fseventsd</string>
                    <string>/Library/Caches</string>
                    <string>/Library/Logs</string>
                    <string>/System/Library/Caches</string>
                    <string>/System/Library/Extensions/Caches</string>
                    <string>/private/var/log</string>
                    <string>/private/var/spool/cups</string>
                    <string>/private/var/spool/fax</string>
                    <string>/private/var/spool/uucp</string>
          </array>
          <key>systemFilesExcluded</key>
          <false/>
          <key>userExclusionPaths</key>
          <array>
                    <string>/Users/USERNAME/Pictures/cam_in</string>
                    <string>/Users/USERNAME/Epsilon</string>
                    <string>/Users/USERNAME/Desktop</string>
                    <string>/Users/USERNAME/Pictures/cam_out</string>
          </array>
</dict>
</plist>

Time Machine not backing up iPhoto changes (Events, pictures, etc..)

So I finally decided to buy a external hard drive (WD) and backup some of my data to it using Time Machine. The initial backup went well with no problems but what I noticed is as I added events and pictures they were not appearing in Time Machine.
I could open time machine and view that my iPhoto had the current events when the date selected was "Today (now)", but as I went back in time the events that SHOULD of been there were not.
Browsing the folders on the backups showed the iPhoto database to be 13.5gb when actually the new size on my iMac was 19.5gb.
So why does Time Machine not detect these changes? For my backups I have excluded all folders except for the Users folder which contains the iPhoto library. Time Machine is not detecting the changes and backing it up. How can I fix this?

Yeah. At first I thought it was:
http://web.me.com/pondini/Time_Machine/D5.html
Because I was doing that earlier. But then realized I did repair permissions, not disk. But anyways decided to reboot (because I haven't up to this point).
Once it came back up I tried doing another backup. Didn't see it. Opened iPhoto again and exited it (checked Force Quit to make sure it wasn't open). Told it to do a BACKUP NOW. This time it saw a difference of like 7mb.
After it was done, went to iPhoto -> File -> Browse Backups. Went back a couple minutes when I did the backup and my event now has a place holder within the Events but it is pure black. I double clicked the event and it opened up and saw there were 3 files in there. They had default icons and were not showing as pictures like they were. (even though they display fine in iPhoto).
Time Machine seems very flakey to me. My machine is fully updated also.

Time Machine not backing up both internal hard drives on 2011 iMac?

I have a 2011 iMac with two internal hard drives---a 2TB HDD and 256GB solid state.
I plugged in a 3TB FW800 external to use with Time Machine.
Based on adding up the used space from both drives as seen in disk utility (totalling 1537.36 GB), it doesn't appear that Time Machine is backing everything up (total backup of 1.49 TB).
Any ideas?
Thank you,
Taylor

Launch the Terminal application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Terminal in the page that opens.
Drag or copy — do not type — the following line into the Terminal window, then press return:
sudo tmutil compare
You'll be prompted for your login password, which won't be displayed when you type it. You may get a one-time warning not to screw up.
The command will take at least a few minutes to run. Eventually some lines of output will appear below what you entered.
Each line that begins with a plus sign (“+”) represents a file that has been added to the source volume since the last snapshot was taken. These files have not been backed up yet.
Each line that begins with an exclamation point (“!”) represents a file that has changed on the source volume. These files have been backed up, but not in their present state.
Each line that begins with a minus sign (“-“) represents a file that has been removed from the source volume.
Files that you’ve excluded from backup, or that are excluded automatically, are ignored.
At the end of the output, you’ll get some lines like the following:
Added:
Removed:
Changed:
These lines show the total amount of data added, removed, or changed on the source(s) since the last snapshot.

Time Machine not backing up full drive

On my macboook pro late 2009 model with mountain lion 10.8.2 time machine will not back up my full drive. I have 56gb use out of 250gb and only 8gb gets backup . How can i get time machine to back up the full 56gb on the first time of setup time machine? I am useing a hard drive connected to my airport extreme. I have the hard drive setup for one big parition. The size of the usb hard drive is 2tb. I have two users on my airport extreme that can access my usb hard drive. One for my macbook pro and one for my mac mini. My mac mini late 2011 model with mountain lion 10.8.2 useing time machine it can back up the full drive. On my mac mini i have 2.5gb used out of 500gb and time machine can back up 2.5gb on the first time i started time machine. But this is not the case for my macbook pro it will not back up the full used space on the first time i setup time machine. How can i fix this so that time machine will backup the full used space?

If you have more than one user account, these instructions must be carried out as an administrator.
Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Console in the icon grid.
Make sure the title of the Console window is All Messages. If it isn't, select All Messages from the SYSTEM LOG QUERIES menu on the left. If you don't see that menu, select
View ▹ Show Log List
from the menu bar.
Enter the word "Starting" (without the quotes) in the String Matching text field. You should now see log messages with the words "Starting * backup," where * represents any of the words "automatic," "manual," or "standard." Note the timestamp of the last such message. Clear the text field and scroll back in the log to that time. Select the messages timestamped from then until the end of the backup, or the end of the log if that's not clear. Copy them (command-C) to the Clipboard. Paste (command-V) into a reply to this message.
If there are runs of repeated messages, post only one example of each. Don't post many repetitions of the same message.
When posting a log extract, be selective. Don't post more than is requested.
Please do not indiscriminately dump thousands of lines from the log into this discussion.
Some personal information, such as the names of your files, may be included — anonymize before posting.

Time machine not backing up since installing Lion

Since installing Lion, time machine get stuck "preparing for backup" but never goes through with it.
Need guidance. Thanks.

Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ If you’re running Mac OS X 10.7 or later, open LaunchPad. Click Utilities, then Console in the page that opens.
Select "system.log" from the file list. Enter "backupd" (without the quotes) in the String Matching text field. Post the messages from the last backup, beginning with "Starting standard backup." Post the log text, please, not a screenshot.
If there are runs of repeated messages, please post only one example of each. Do not post many repetitions of the same message.
Some personal information, such as the names of your files, may be included — edit that out, too, but don’t remove the context.

Time Machine not backing up iTunes folder

Hi.
I am having an issue with Time Machine on my MBP running 10.5.5. I currently have 2 TM backups on a 400gb external hard drive. Each backup is roughly 45gb. However, both times, my iTunes folder not been backed up. I checked the Time Machine options and nothing is being excluded.
Is there a way to make sure this folder is backed up?
Thanks,
markzegarelli

Sorry for the lack of clarity. I mean that Time Machine has backed up 2 times to this drive.
To expand a bit further, when I browse the disk in Finder, and navigate to where the back up of the music folder should be, (eg. backups.backupdb/<computer name>/2008-10-27-030029/<hd name>/Users/<user>/Music) all I see is an alias. Clicking the alias presents an error which says "The alias 'Music' could not be opened because the original item can not be found."
Thanks again.

Time Machine not backing up all data

Hello All,
I just bought a Time Capsule 2TB and have Macbook pro early 2011 (running Lion OSX). I wanted to do to a time machine backup. Everything went well. I got it connected good and the backup started very weel. My HDD is about 400 GB and when the time machine started back up it started with data and the progress bar showed the total data to be back up (400GB), but then it backed up only 30 GB out of 400 GB.
I have most of my files in iphoto and ivideo. Is this normal? Why didnt TIme machine did not back up all 400GB?
Any idea?

Then there are two possibilities:
The backup failed, but you didn't see the message. See #C2 in Time Machine - Troubleshooting. It will show you how to locate the message(s) that describe the problem, then help you fix it. If that doesn't help, post back with details, including all the messages.
Or, some things didn't get backed-up. A partial explanation could be iPhoto -- if the iPhoto app is open when a backup runs, Time Machine may not be able to back up your iPhoto library. It will attempt to "catch up" the next time, but in the meantime you may not have any backups of it.
That's unlikely to be the whole difference, though. Does the figure of 400 GB seem reasonable to you -- can you account for most of it?

HT201250 Backup too large & time machine not backed up for over a year.

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