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FAQ: unexpectedly slow performance

Posted: Tue Aug 20, 2019 9:47 pm
by katsura
if other process uses the disk while you measure the disk performance, you get slower than expected performance.
  1. Time Machine: make sure Time Machine is not backing up (accessing the storage device). this usually happens every hour if you have Time Machine enabled. you can check the Time Machine menu on the menubar if the backup is running or not. the OS accessing other disks could (and does) also affect the performance of the disk you are trying to measure.
  2. Spotlight indexing: mds, mdsync, md_stores, mdworker, mdworker_shared (anything from Metadata.framework) will affect the disk access performance.
i usually run "iostat -w1" in Terminal (or over ssh) to monitor the disk access activities and run the performance measurement while there are no other activities.