Ext3 users - Feb 2010 - Overwrite Mechanism

Hi all,
 
i wanted to ask you all about the exact overwrite mechanism used in
ext3; is the information in the datablocks overwritten or written to a
new location and the information in the referring inode is changed? Is
it depending on the application used (and the functions it calls) or
independent from that?
 
Please don't hesitate to go into further details and thanks for your
help!
 
cheers,
flo


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On 2010-02-24, at 01:49, Schrittesser, Florian wrote:
> i wanted to ask you all about the exact overwrite mechanism used in  
> ext3; is the information in the datablocks overwritten or written to  
> a new location and the information in the referring inode is  
> changed? Is it depending on the application used (and the functions  
> it calls) or independent from that?
>
> Please don't hesitate to go into further details and thanks for your  
> help!

It depends on what your application is doing.  If it is opening the  
file with open(O_TRUNC) then writing it, the new data is written to  
wherever it is allocated.  If O_TRUNC is not used, then the data is  
written into the same blocks as were previously allocated to the file.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.