Fix Slow Time Machine Backups on a Mac

Mar 19, 2016 - 51 Comments

Fix a slow Time Machine backup

The amount of time it takes to complete a Time Machine backup depends on a variety of things, like the amount of data being backed up, the destination drive speed, the speed of the internet connection if the backup is going to a Time Capsule, whether it’s the initial backup or a delta backup of changes made, amongst a variety of other factors. You’ll typically get an idea of how long a Time Machine backup should take to complete after it has ran a few times on a Mac, so if you discover suddenly that the Time Machine backup is taking an extremely long time or is backing up unusually slow, follow the troubleshooting steps below to speed things up.

How to Troubleshooting Abnormally Slow Time Machine Backups

Note these tips are aimed at resolving unusually slow backups, not failed backups, not delayed backups nor the stuck on “Preparing backup” issue.

1: WAIT! Are you sure the backups are going slower than usual? Let it run over night if in doubt

This may sound a little silly, but are you sure the backup is abnormally sluggish? Is the backup actually going unusually slow, or is there simply a lot of data being backed up? This is particularly important for the first backup a Mac has made, or a notable amount of time has passed between backups. It’s also true if you download or create a lot of media on the Mac, which can take up many GB of disk space, and as a result can take a while to backup.

If you aren’t certain about this, or you have any doubt, just let the Time Machine backup run overnight.

2: Stop & Start the Backup

Sometimes simply stopping, waiting a few minutes, and starting the backup to Time Machine will remedy speed issues.

  1. Pull down the Time Machine menu bar item and choose “Cancel Backup”
  2. Wait a few minutes, then go back to the Time Machine menu item and choose “Start Backup”

If you check on the elapsed data transfer and time remaining to completion, and things look like they’re cruising along as usual, then you’re good to go.

3: For Time Capsule Backups, Connection & Distance Matter

If Time Machine is unusually slow and the backups are being completed over wi-fi with a Time Capsule, you’ll want to insure the wi-fi connection is strong and that both devices are reasonably near one another.

Often this means simply placing the computer in the same room with no obstructions between the devices, so that there is a strong connection and minimal interference.

4: Reboot into Safe Mode & Back Again

Another trick to remedy sluggish Time Machine backups involves booting the Mac into Safe Mode, then rebooting the Mac back into regular OS X mode, and starting the backup again:

  1. Reboot the Mac and hold down the Shift key after you hear the startup chime, this will force the Mac to boot into Safe Mode
  2. Let the Mac boot into safe mode as usual, when the desktop appears let it sit a moment for everything to continue loading, then reboot the Mac again this time as usual, by going to the  Apple menu and choosing “Restart”
  3. When the Mac boots again into regular mode, start a backup manually with Time Machine

This is a bit of a weird solution to abnormally slow Time Machine backups but it often works when there is seemingly no particular issue causing the backup to be slow in the first place. The trick has been around for ages since the introduction of Time Machine, and since it still works to this day suggests something.

Know of any other tips to speed up unusually slow Time Machine backups? Let us know in the comments.

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Posted by: Paul Horowitz in Mac OS X, Tips & Tricks, Troubleshooting

51 Comments

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  1. Wharf Xanadu says:

    Stopping the backups then rebooting into safe mode and rebooting back into normal and starting the backup again works every time. It has worked since OS X Ancient Release Cat and there must be a bug. Now it still works to fix the problem and speed up a backup.

    • Sunil Kumar says:

      I was also facing very slow TM backup

      Used this tip
      Go to a Terminal and enter:

      sudo sysctl debug.lowpri_throttle_enabled=0
      For me, this speed it up from 72 hours to ~4 hours on an filesystem with 2.5 million files.

      It’s also a good idea to re-enable the throttling after your backup finished successfully with the following command

      sudo sysctl debug.lowpri_throttle_enabled=1

      My case was solved.

      • bhu Boue vidya says:

        OMG thank you so much that is a fantastic tip. it has sped up my backups by an *extraordinary* amount

      • aminfosystems says:

        OMG, this worked for me as well. Why? How?

        What are the pros/cons here. This was a night and day change.

      • Graze says:

        Thank you so so much!!! I have spent a ridiculous amount of time and have tried so many different ways to get Time Machine Backups to work properly, this has improved the speed x10 at least – Finally some relief :)

      • manuel says:

        Hi, How do i disable this later? Thanks

        • Tim says:

          This command does seem to be helping. I bought a new 8TB backup disk for my iMac and the initial backup of about 2 TB worth of data ran for over 10 days and had only backed up about 350 GB. At that rate, it would take about two months to complete.

          By the way, you don’t have to reboot to disable this option. If you look at the provided command:

          sudo sysctl debug.lowpri_throttle_enabled=0

          The =0 part disables the throttling. Note the double-negative, so this in fact lets Time Machine run at full speed. To re-enable throttling, you can simply change the 0 to a 1 :

          sudo sysctl debug.lowpri_throttle_enabled=1

          I’m enabling throttling (=1) during my work day and disabling it (=0) at the end of the day, until this initial backup is completed.

          If you forget what state the parameter is in, run the command without a setting:

          sudo sysctl debug.lowpri_throttle_enabled

          and it will show you the current value of the debug.lowpri_throttle_enabled parameter.

          Thanks again to Sunil Kumar for the pointer.

      • Stephen says:

        Holy Crap!!!
        Was = 22hrs
        After terminal command and roughly 30 seconds
        Now = 9hrs
        After 4 minutes = 6hrs

      • Cheers, from 11 to 3 hours !

      • JFairweather says:

        Backing up startup SSD and fast internal HD. 1.8 TB total over USB3 to Voyager dock / 4TB WD Black.

        First 3-4 minutes running from 500K to 6MB/second. Afterwards jumped to 160 MB/second.

        I understand the purpose of throttling in certain contexts (mother-in-law, annoying dog next door, etc.) but I’m wondering about the purpose of throttling on a Mac.

      • Adrian Glamorgan says:

        My mac says

        sudo: syscti: command not found

        Can you help?

        Thanks

      • Erik Stenhammar says:

        Thank you!

        Left my mac to backup over night yesterday and woke up today to see that just 9 gb!? out of 640 gb was backed up after 11 hours… Normal according to Apple support…

        Tried this and just finished backup of the totalt 640 gb in less than 5 hours so THANK YOU ❤️

      • Mark says:

        Brilliant! Massive difference in backup speed, thank you!

      • Coldog says:

        mine says

        sysctl:must specify -w to set variables

        Can you help?

      • Kickroot says:

        My god this was wonderful. It takes effect instantly (no need to restart the backup) and I immediately saw a 50x increase in backup speed. Literally, it went from less then 1MB/s to 50MB/s (as shown on Activity Monitor).

        You’re mileage will vary, of course.

  2. Bill McCullough says:

    I like to run DiskWarrior on Time Machine backups from time to time. Optimizing the huge TM directories has helped me when TM seems slower than it should be.

  3. Alex says:

    What if yopu ca not boot into Safe Mode?

    • Douggie says:

      Everyone can boot into Safe Mode. That’s like saying what if ‘yopu’ can not power on. If the Mac works, safe mode works. Is yopu your name for your Mac? Kind of weird, but ok.

  4. Ian says:

    Thanks for this and many other excellent articles – I frequently visit your website!

    However, this particular problem with EXTREMELY slow time-machine backups persists whatever I try to do, including all four of your suggestions, and I have also followed other several forums with various suggestions, none of which help. It seems to be a serious problem in Mac OS that has not been resolved for a long time. Right now I am in the middle of a new back-up which has been going on for more than five hours, and is still only halfway. I wish Apple would wake up to this one!

  5. Phred says:

    I am a nacbook owner who is not a mac fan.

    I seldom use my macbook in OS-X. I have a Linux VM where I do 80% of my work. I only run Microsoft office in OS-X.

    I also killed spotlight so it no longer indexes my hard drive.

    Can I still run a full tine machine backup once in a while?

    • SixnaHalfFeet says:

      Phred, you do realize that Mac OS X is a Unix based os and so can do everything you do in Linux, right? (with maybe only a couple minor exceptions)

      Anyway, to answer your question, you can run time machine anytime you want.

      The easiest way is to just set it to do automatic backups and connect an external hard drive. It will backup whenever your external is connected and won’t backup when it isn’t.

      • Phred says:

        OS-X is unix with an “attitude”, that rubs me the wrong way.

        Anyway, will it do a “full backup”. I heard it dies incrimental backups based on the results of the index searches. My mac has no index files because it laxks spotlight.

        Thx

        • Brian says:

          Time Machine uses Spotlight to do indexing for the backup. Depending on how you disabled Spotlight, Time Machine may also be disabled. If your Spotlight is having problems those same problems can crop up in Time Machine. Time Machine is file based rather than block based and will be slow with a large VM hard drive file. You can exclude the file.

  6. Xfr says:

    “the speed of the internet connection if the backup is going to a Time Capsule”. I did not think that Time Capsuke supports remote backups over the internet. Or perhaps the author means “Wifi speed”?

  7. DB says:

    If your TM backups have become slow recently and seem to be getting slower, the backup hard drive might be ‘dying’. The slowness could be due to bad sectors and excessive numbers of read/write fails and retries. Best to always maintain a second backup.

  8. Val says:

    Hi all,

    I just upgraded my MacBook Pro (2010 model) from Mountain Lion to El Capitan. I find that the El Capitan works much slower for me–which prompted me to order an SSD to install ASAP.

    Meanwhile, another significant problem I have encountered is the slow Time Machine backup. My last backup was done on the Mountain Lion OS — so given the brand new OS, does this mean that essentially time machine is trying to back up my entire Mac HD (414gb) all over again (hence the extremely slow preparation time) instead of ‘picking up from where I left off’? Any suggestions would be much appreciated

    • int says:

      Yes Time Machine now has to backup the new OS installation as well as your files, it may take a while to complete that.

  9. Adam says:

    In my instance it was spotlight that was stalling the backup. Stop spotlight from searching your time machine drive and hey presto, backups should take no time.

  10. Eric says:

    Shutting down and re-starting perhaps works better.

    Apple should fix this. Its obviously the algorithm setting itself tasks which accumulate over time.

    If re-starting fixes it, damn it Apple, 8 billion ought to fix it.

    Please PAY ATTENTION TO THE MAC

  11. Colin says:

    I rebooted normally and left running overnight to discover that after hours of activity only ~800 MB had been transferred to my Time Capsule!!!! stopping the backups then rebooting into safe mode and rebooting back into normal and starting the backup again worked for me – shocking!!!

  12. Paul Gilbert says:

    I had slow backup running OS x Mavericks 10.9.5 on a 2009 iMac doing an initial backup to a new Seagate 3TB expansion drive using USB 2.0. Speed was about 2 GB per hour. Also, Time machine was displaying “calculating time remaining” but never presented an answer. (Perhaps it didn’t want to admit the backup would take 300 hours.) I took a number of the actions recommended on various websites so I’m not sure which one did the trick. I did a permission fix on my drive using disk utility. I rebooted into safe mode. I’m guessing the last item helped the most since it took about 15 minutes so it might have been fixing something significant. After the fixes my first backup took less than 6 hours so it was backing up at a rate of over 100 GB per hour.

  13. Earl Zubkoff says:

    (I’m sharing my solution on several forums where this issue has been posted.)

    After upgrading from Mountain Lion to El Capitan on a Mac Pro, I saw a speed reduction of over 90%
    in the Time Machine backup process. I use an external USB3/FW800 backup drive; both interfaces exhibited the problem. I followed other users’ advice, disabling virus scanning and Spotlight on the target drive, disconnecting peripherals, stopping & starting, setting Sleep to “Never,” etc. (I did not try any of the Safe Mode procedures or Terminal system hacks.) I got negligible improvement.

    Here’s what worked. I disconnected from the network, in my case by unplugging the ethernet cable but others may need to turn off wifi. Then I turned off the full-time virus monitoring on the whole machine. (I use Sophos, where that function is called “On-Access Scanning”.) The full speed was immediately restored.

    Obviously this won’t work for anyone who backs up over their network or wifi — you’d be vulnerable while virus monitoring is off. Or for those who use the continuous Time Machine scheduling. But if, like me, you use Time Machine for occasional manual backups (I go once a week), you’ll be happy.

    And perhaps with this clue Apple can modify its Time Machine code to improve its dismal performance.

  14. Troels says:

    My issue was the antivirus in El Capitan.

    I have Sophos antivirus.

    Disabling the anti-virus, the transfer rate went dramatically up. If I in Sophos specified the folders:
    /Volumes/Data-1/xxx Macbook Air.sparsebundle/
    to be excluded, I got the same effect having the antivirus on.

  15. Fred (Brian) Walters says:

    I had exactly the same problem. When I added my back-up drive to Sophos’s ‘Excluded Items’ (go to Sophos Preferences), the transfer rate went to what I’d expect…

    About 4GB in about 5 minutes rather than about 200MB in 4 hours!

  16. Alex Spathis says:

    My WD My Cloud Mirror was extremely slow to backup to my iMac 4k as reported in many many locations. I found this thread and others that discussed using the terminal, creating sparse bundles etc etc

    I was backing up about 800 Gb using Apple Time Machine under El Capitan version of Mac OS

    I finally just upgraded to the latest firmware for the hard drive and a backup that had run for over a week (!!!) and was still running took less than 7 hours after the firmware upgrade.

  17. Antonio says:

    Have everyone tried to switch every antivirus off?

  18. Antonio says:

    It worked in my case in improoving backup speed

  19. Craig says:

    I have been fighting this slow backup for awhile now. I finally found what works for me. I have Avira protection on my MABook Pro. I turned off the Avira real time protection and now my Time capsule works likes a champ.

    I hope this helps anyone out there!!

    • Joyz says:

      I have Avira “real time protection” turned off and I’m still seeing 12 GB taking over an hour on a 2TB Backup Plus. I upgraded to OS Sierra – was thinking that had an effect. Had to do a full backup.
      Did you upgrade your MacBook Pro?

  20. Mac User says:

    ——RESOLVED——

    I had a nightmare trying to figure out why my backup was slow, however finally figured it out.

    STUPID Antivirus, I switched off the antivirus and magic, it was fast as lightning.

    It seems anything that is scanning files or external drives will slow Timemachine backup’s to a snails pace, I had my Mac running for 48 hours and only 1gig backed up.

    If you switch off antivirus/other scanning software just until the backup is complete then you should have no issues.

  21. Mac_User123 says:

    ——RESOLVED——

    I had a nightmare trying to figure out why my backup was slow, however finally figured it out.

    STUPID Antivirus, I switched off the antivirus and magic, it was fast as lightning.

    It seems anything that is scanning files or external drives will slow Timemachine backup’s to a snails pace, I had my Mac running for 48 hours and only 1gig backed up.

    If you switch off antivirus/other scanning software just until the backup is complete then you should have no issues.

  22. Paul says:

    I also suffered from very slow backups. My problem was that Sophos security software was scanning – something… So, I turned off On-Access Scanning in Sophos preferences. Don’t know how to turn off backup scanning if in fact this was happening. Backing up went from less than 1 Gb per hour to 14+ Gb per hour!

    Does anyone know how to eliminate on-access scanning for backups to a time capsule?

    Many thanks. Paul

  23. martinhrvn says:

    My backups were very slow recently, even the “Preparing backup” took several hours and I found out that in my case this was due to disk errors.

  24. Stephen White says:

    I discovered that Kaspersky Internet Security was the problem. As soon as I turned off protection, the backup time plunged (about two hours to backup 300 Gbytes of data). Solution: You can tell Kaspersky to ignore TM. Here is the official solution:
    “STEP 1: Please add this to the Trusted Zone in Kaspersky to exclude it from scans:
    Open Preferences: http://support.kaspersky.com/us/12555
    Click on ‘Threats’ along the top of the preferences window
    Click the ‘Trusted Zone…’ button near the bottom right.
    Click the + button on the bottom left.
    Locate what you are looking to exclude, and click the ‘OK’ button.
    Close out of the Preferences window, and test if the issue persists”

    Presumably this approach will work for other anti-virus software.

  25. sakeboy says:

    Thank you! The terminal command worked for me! Was doing 1GB per day on a 2016 Macbook Air w/ USB3 external drive, now doing closer to 1GB per minute. At 500GB of data to transfer, this was a lifesaver.

  26. rich hem says:

    Can this terminal throttle command be run whilst backing up. Been backing up for two days half way through, not sure if i want to stop it and try the command

    sudo sysctl debug.lowpri_throttle_enabled=0

  27. Sadly this terminal throttle command did not help me. There is something else that is happening with Time Machine that needs genuine Apple Support. URGENTLY!!
    I have a 2017 MacBook Pro with 1TB SSD that reads/writes at speeds in excess of 2000 MB/sec, trying to back up a lousy 250 gbs to a Thunderbolt 3 connected 1 TB external SSD that reads/writes at speeds in excess of 500 MB/sec …… and it sitting there taking DAYS. It should be minutes, not even hours.
    Anyone have better solutions?
    I do not ever remember such slow backups from earlier Mac OS versions, and they were with much slower processors and HDD’s backing up more data (most of my stuff is up in iCloud now).

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