My MBP has only 8GB RAM, and whenever it does an hourly Time Machine backup it starts to crawl. This causes the backup to take a very long time for not much data.

At this point, Swap Memory usage is up to 12GB which is way above my usual/everyday Swap Memory usage of < 2GB.

Once the backup is over half way through, Swap Memory usage is at roughly 5GB until it is finished when it drops back to normal.

Is it usual for backupd to need so much memory?

TheTimeMachineMechanic gave this diagnostic, confirming that 878MB took 35 minutes!

Analysis from 2019-01-30 12:23:58 +0000 to 2019-01-30 14:23:58 +0000 for 2 hours:
Backing up to /dev/disk2s2: /Volumes/Tardis/Backups.backupdb
on which there were 228.35 GB available.
Started 1 auto backups, and 0 manual backups; completed 1 backups successfully,
last backup completed successfully 7.0 minutes ago,
backed up a total of 7193 files, range 1884 to 5309 in each backup,
total data for each backup was 335.4 MB, 878.3 MB.
Times taken for each auto backup were 34.9 minutes,
Created 1 new backups, and deleted 0 old backups,
Created 2 new snapshots, and deleted 0 old snapshots,
cancelled 2 backups.
No error messages found.

My system:

  • MacBook Pro (Retina, 13-inch, Early 2013)
  • 3 GHz Intel Core i7
  • 8 GB 1600 MHz DDR3
  • LaCie Rugged 1TB Thunderbolt drive

Edit: April 2019

Usually my Mac is at somewhere less than 2GB of swap memory, but during a Time Machine backup it balloons to ~20GB, throttled - I imagine - only by the free space on my drive (~30GB).

My computer slows to a crawl and is unusable until the backup either completes or fails. The screenshot shows a backup of only 250MB!

During all of this, there is no one process that is running away with memory.

So, what's going on? And how can I avoid this?

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  • Going to take some spelunking to dig into your memory usage. Are you able to reproduce this if you make a brand new user account that starts nothing - disable auto log in and reboot - start with the clean user and run Time Machine? My thinking is it's the other things you have running and not TM that results in the balloon. Of course TM pushes your system into swap, but it's probably not the "cause" is my thinking. – bmike Apr 2 at 12:16
  • I'll try that. Somebody on Twitter suggested it could be the complexity of my existing backup data, that causes TM/macOS to struggle working with all those aliases. So I'll also see if I can find a spare drive to try a fresh backup to a blank disc on my account. – Matt Sephton Apr 2 at 16:45
  • Just have not had time to do anything about this (so only backing up once a week). – Matt Sephton Apr 8 at 17:37
  • @bmike I recently cleared out a load of old files on my Mac and went from ~5% free space to >15% free space and this issue seems to have gone away (a couple of days regular hourly backups so far). The CPU still works hard and fans come on, but swap memory never reaches silly levels. This all makes no sense, so I'll wait a while longer to confirm. – Matt Sephton May 31 at 12:56
  • @bmike false alarm, it's still doing it, sometimes. gah this is annoying. – Matt Sephton Jun 6 at 0:39

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