Re: fsync() Performance Issue

[Hans Reiser <reiser@namesys.com>]

Valdis.Kletnieks@vt.edu wrote:

>On Mon, 29 Apr 2002 19:56:59 +0200, Matthias Andree <ma@dt.e-technik.uni-dortmund.de>  said:
>
>  
>
>>Barring write cache effects, fsync() only returns after all blocks are
>>on disk. While I'm not sure if and if yes, which, Linux file systems are
>>affected, but for portable applications, be aware that sync() may return
>>prematurely (and is allowed to!).
>>    
>>
>
>And in fact is the reason for the old "recipe":
>  # sync
>  # sync
>  # sync
>  # reboot
>
>On the older Vax 750-class machines, sync could return LONG before the blocks
>were all flushed - the second 2 sync's were so you were busy typing for
>several seconds while the disks whirred.  Failure to understand the typing
>speed issue has lead at least one otherwise-clued author to recommend:
>  # sync;sync;sync
>  # reboot
>
>(the distinction being obvious if you think about when the shell reads the
>commands, and when it does the fork/exec for each case....)
>
>  
>
Finally I understand this.  Doing more than one sync always seemed 
mysterious to me.;-)

Thanks Matthias.

Hans