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strange filefrag output on btrfs

DISCUSSION Andreas Philipp 4 participants 6 messages Jun 11, 2011 – Jun 14, 2011 Btrfs file system

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Andreas Philipp

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#0 lore raw

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Hi,

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

Thanks,
Andreas
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#1 lore raw
Quoted 8 lines · Andreas Philipp

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?

david

author
#2 lore raw

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Quoted 5 lines · David Sterba
Quoted 4 lines · Andreas Philipp

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.

Quoted 7 lines
Quoted 4 lines

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

Thanks,
Andreas
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#3 lore raw
Quoted 21 lines · Andreas Philipp

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Quoted 5 lines · David Sterba
Quoted 4 lines · Andreas Philipp

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.

Quoted 7 lines
Quoted 4 lines

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.

Quoted 11 lines

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.

author
#4 lore raw

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Quoted 33 lines · Li Zefan
Quoted 22 lines · Andreas Philipp

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Quoted 7 lines · David Sterba
Quoted 5 lines · Andreas Philipp

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.

Quoted 7 lines
Quoted 4 lines

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.

Quoted 7 lines

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.

Quoted 8 lines

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.

Andreas
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#5 lore raw
In reply to Li Zefan
Quoted 2 lines · Li Zefan

There are two ways to calc the extent number, depending on whether verbose option is turned on or not.

To me that's very counter intuitive!

Maybe another way to do that is to name those two values differently and in verbose mode report them both so people can see that there is a match ?

cheers,
Chris

Signature · 1 line
 Chris Samuel  :  http://www.csamuel.org/  :  Melbourne, VIC