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   The Natural Philosopher  writes:   
   > On 02/08/2024 15:03, Björn Lundin wrote:   
   >> dd'ing 500 Gb to an ssd disk, I've seen sync taking 30 s or more   
   >> and sync is of course started AFTER dd is done   
   >> So - how do you know it is done its internal business?   
   >> Not all drives have blinking LEDs   
   >> sync makes it easy to know   
   >   
   > Even sync may not be enough.   
   > SSDS/NVM have their own internal  caching.   
      
   The sync syscall (and command) will flush those too.   
      
   Unless you’ve paid extra for a drive with a huge cache I would expect   
   the extra delay while the on-drive cache is flushed to be absolutely   
   tiny in human terms, and certainly tiny compared to flushing the OS’s   
   cache, which can be multiple gigabytes.   
      
   References:   
   * https://www.kernel.org/doc/Documentation/block/writeback_cache_control.txt   
   * https://linux.die.net/man/2/sync   
   * https://github.com/torvalds/linux/blob/master/fs/sync.c#L87   
      
   --   
   https://www.greenend.org.uk/rjk/   
      
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