Need a time machine for your TM backups?

Part of the issue is that low priority input/output-operations (I/O) now seems to get throttled heavily.   In bash, type:

• sudo fs_usage backupd

look for entries labeled throttled.  If you see them, the backup is throttled. 

So if you have a ton of files, just the time it takes to do the I/O takes forever, even if the files are small (because it performs a bunch more I/O operations around xattrs etc. than it used to).

Go to a Terminal and enter:

• sudo sysctl debug.lowpri_throttle_enabled=0

If you want to make it permanent across reboot, you can do the following.

..Add the line to /etc/sysctl.conf

or..

​
create a file under /Library/LaunchDaemons/fix-el-capitan-slow-time-machine-speed.plist

<?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>Label</key> <string>fix-el-capitan-slow-time-machine-speed</string> <key>ProgramArguments</key> <array> <string>/usr/sbin/sysctl</string> <string>debug.lowpri_throttle_enabled=0</string> </array> <key>RunAtLoad</key> <true/> </dict> </plist>

make sure the file belongs to root:

• sudo chown root /Library/LaunchDaemons/fix-el-capitan-slow-time-machine-speed.plist

issue the command:

• sudo launchctl load /Library/LaunchDaemons/fix-el-capitan-slow-time-machine-speed.plist