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List:       bacula-bugs
Subject:    [Bacula-bugs] [bacula 0001704]: FIOBMAP suboptimal for sparse files
From:       Mantis Bug Tracker <nobody () baculabugs ! unixathome ! org>
Date:       2011-03-17 11:30:46
Message-ID: dfdd78e701bec145ee07c999e6d02cba () bugs ! bacula ! org
[Download RAW message or body]


The following issue has been REOPENED. 
====================================================================== 
http://bugs.bacula.org/view.php?id=1704 
====================================================================== 
Reported By:                stoatwblr
Assigned To:                ebollengier
====================================================================== 
Project:                    bacula
Issue ID:                   1704
Category:                   File Daemon
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     feedback
====================================================================== 
Date Submitted:             2011-03-08 17:36 GMT
Last Modified:              2011-03-17 11:30 GMT
====================================================================== 
Summary:                    FIOBMAP suboptimal for sparse files - FIOEMAP
better.
Description: 

  Recommended LWN article: SEEK_HOLE or FIEMAP?
  http://lwn.net/Articles/260795/

  "When an application wants to know how a file is store in the disk (for
  example, a backup application that wants to know if a file is a sparse
  file and wants to avoid backing up the hole) it uses the fibmap ioctl.
  But this ioctl is suboptimal - the ioctl can only be asked for a block
  at a time, which is too expensive for big files. The FIEMAP ioctl, in
  the other hand, returns a list of extents."

Many other OSes have the same (or equivalent) ioctl.


Using FIEMAP would allow automatic handling of sparse files without incurring
the speed penalties associated with FIOBMAP



Steps to Reproduce: 

Create sparse files, access using FIOBMAP and FIOMAP, time the difference.


====================================================================== 

---------------------------------------------------------------------- 
 (0005800) ebollengier (administrator) - 2011-03-17 10:19
 http://bugs.bacula.org/view.php?id=1704#c5800 
---------------------------------------------------------------------- 
Thanks for your proposal, unfortunately, we deal only with Bugs in this tool.
For new features, see www.bacula.org -> New Features.

For your information, Bacula already supports Sparse file with a very simple and
portable scheme. Unless you show us (with real data) that your idea improve the
throughput or the cpu usage by a reasonable factor, we won't change the current
code. 

---------------------------------------------------------------------- 
 (0005804) stoatwblr (reporter) - 2011-03-17 11:30
 http://bugs.bacula.org/view.php?id=1704#c5804 
---------------------------------------------------------------------- 
I suspect you don't realise how much of a slowdown the current setup imposes -
it's in the region of 50%.

Additionally: When discussing things with Kern he specifically requested I file
this kind of thing in Bugzilla so there is a record of it. 

Issue History 
Date Modified    Username       Field                    Change               
====================================================================== 
2011-03-08 17:36 stoatwblr      New Issue                                    
2011-03-09 09:38 mnalis         Issue Monitored: mnalis                      
2011-03-17 10:19 ebollengier    Note Added: 0005800                          
2011-03-17 10:19 ebollengier    Status                   new => closed       
2011-03-17 10:19 ebollengier    Assigned To               => ebollengier     
2011-03-17 10:19 ebollengier    Resolution               open => no change
required
2011-03-17 11:30 stoatwblr      Note Added: 0005804                          
2011-03-17 11:30 stoatwblr      Status                   closed => feedback  
2011-03-17 11:30 stoatwblr      Resolution               no change required =>
reopened
======================================================================


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