[CentOS] Preventing the nightly backup from disturbing the cache

Mon Apr 24 23:03:49 UTC 2006
Adam Gibson <agibson at ptm.com>

Steve Bergman wrote:
> David Mansfield wrote:
>> I don't think this is necessarily safe to do.  O_DIRECT adds 
>> additional requirements to the memory buffer's alignment and file 
>> position alignments.  Unless you have audited the 'tar' source code, I 
>> think this is a bad idea.
> Actually, I was just getting ready to follow up.  Although the tar 
> archive structure looks fine, and most of the files are OK, I HAVE FOUND 
> CORRUPTION IN SOME FILES.  So don't use that patch.

I wonder if the corruption has something to do with needing to ftruncate 
a file if the file does not precisely end at a block boundary(as the 
reference in my previous email mentions).  I would have expected almost 
all files to not end on a block boundary so most of them should have 
been corrupt but most of them were OK you say?

> OK.  If that strategy does not work, how about the earlier suggestion of 
> fadvise?  Would that be safer?  And can anyone provide an example of how 
> fadvise64_64() is actually used?  I'm not a C programmer.
> -Steve

Nice.  Looks like the right solution.