From: invalid@invalid.invalid   
      
   Rich  writes:   
   > Mike Small  wrote:   
   >> I'm noticing places in both Slackware's installer and   
   >> debian-installer where a mkfs run is immediately followed by a   
   >> sync...   
   >>   
   >> [snip]   
   >>   
   >> Is this just a known thing among those who've been around?  mkfs   
   >> isn't truly done and with all bits on disk when it exits?   
   >   
   > It is not just mkfs.  Linux caches writes in RAM, with the data   
   > actually being committed to disk some time later.   
   >   
   > If you want to be sure a write has hit the disk (note, due to on disk   
   > caches, you can never really be /sure/) you need to tell the kernel to   
   > write the cached RAM data out to disk -- that is what 'sync' does.   
   >   
   > Those sync's are not strictly necessary, but are likely present for   
   > safety's sake.  Run the mkfs, then try to make certian all the writes   
   > have been at least sent to the disk controller.   
      
   They are redundant, at least for ext4, since mkfs.ext4 calls fsync on   
   the target device. I’m not going to check other filesystems but the   
   situation is likely to be the same.   
      
   --   
   https://www.greenend.org.uk/rjk/   
      
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