-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 14.06.2011 04:54, Li Zefan wrote: > Andreas Philipp wrote: >> >> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 >> >> On 13.06.2011 13:50, David Sterba wrote: >>> On Sat, Jun 11, 2011 at 05:39:15PM +0200, Andreas Philipp >>> wrote: >>>> On one of my btrfs volumes I see a strange output from >>>> filefrag when run against a particular large (~8GB) file. >>>> filefrag and filefrag -v give me a different number of >>>> extents, see below. >>>> >>>> aph@thor /mnt/nutshell $ sudo filefrag -v funtoo.img | grep >>>> extents funtoo.img: 2624 extents found aph@thor /mnt/nutshell >>>> $ sudo filefrag funtoo.img | grep extents funtoo.img: 2653 >>>> extents found >>> >>> is the file open and being written to? did you run sync before >>> the first command? >> The file is not open. Yes, I have run sync before the first >> command. Now, I tested again with a copy of file but the results >> is more or less the same. >> >> aph@thor /mnt/nutshell $ cp funtoo.img funtoo.1.img aph@thor >> /mnt/nutshell $ sync aph@thor /mnt/nutshell $ sudo filefrag -v >> funtoo.img funtoo.1.img | grep extents funtoo.img: 2624 extents >> found funtoo.1.img: 57 extents found aph@thor /mnt/nutshell $ >> sudo filefrag funtoo.img funtoo.1.img | grep extents funtoo.img: >> 2653 extents found funtoo.1.img: 311 extents found >> > > If you look into the source code of filefrag, you'll know why. > > There are two ways to calc the extent number, depending on whether > verbose option is turned on or not. > > In the verbose mode, it will check if the next extent is adjacent > to the prev extent in the physical position, and in this case they > are considered to be one extent. > > That's why the number returned in verbose mode is smaller. Thank you for this explanation.
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