Re: [Bug-tar] Sparse file performance and suggestions

[Eric Blake]

On 02/06/2011 08:36 AM, Andreas Dilger wrote:
> On 2011-02-06, at 4:49, address@hidden wrote:
>> Currently, tar seems to perform quite sub-optimally when archiving sparse
>> files. I compared the performance of GNU tar and star when archiving a
>> large (~2TB) sparse file. All but about 180MB of the file was holes.
> 
> There was a patch posted a while ago by Bernd Schubert to detect completely 
> sparse files, bit I don't know if there was anything to automatically handle 
> partially sparse files. 
> 
>> Sometimes it's possible to determine the exact hole layout in a file.
>> Apparently that's quite easy in Solaris (SEEK_HOLE, SEEK_DATA) and
>> Windows, less so in Linux (FIEMAP). 
> 
> A question to the tar maintainers - if someone were to write support for 
> FIEMAP detecting holes on Linux would this be acceptable to include upstream?

The patch is already in the process of being written - see coreutils
8.10.  However, there are still some bugs being fleshed out, and adding
support for Solaris SEEK_HOLE, before that code is migrated to gnulib
and imported into tar.

-- 
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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