ext4: Used block count in df

ext4: Used block count in df

[Adil Mujeeb]

Hi,

I have an observation on EXT4 filesystem. I created filesystem of size
1TB, 4TB, and 7TB and then checked the output of df command.

df command showed the number of 1KB blocks used. The result was:
1TB: 204056
4TB: 198680
7TB: 181784

I performed the same on XFS and the result was:
1TB: 32928
4TB: 32928
7TB: 33024

EXT4 result shows with increasing filesystem size, the number of used
blocks decreased. I dont have idea about low level implementation but
I am curious why it is so?

Thanks.

Regards,
Adil

Re: ext4: Used block count in df

[Eric Sandeen]

On 2/7/13 12:39 AM, Adil Mujeeb wrote:
> Hi,
> 
> I have an observation on EXT4 filesystem. I created filesystem of size
> 1TB, 4TB, and 7TB and then checked the output of df command.

Telling us which version of e2fsprogs and which kernel would be helpful,
but:

> df command showed the number of 1KB blocks used. The result was:
> 1TB: 204056
> 4TB: 198680
> 7TB: 181784

extN makes df complicated in several ways.

It reserves blocks for the superuser (5% by default) and also uses a lot
of blocks up-front for filesytem metadata - inode tables, block bitmaps,
and the like.

But what you are seeing here is this:

It also defaults to "bsd df" which does not count filesystem
metadata when telling you about the number of blocks used.  So in theory,
a freshly made fs should actually tell you 0 blocks used, I think.

Looking at the dumpe2fs output for the 4t file, I see:

# dumpe2fs -h 4tfile-ext4 | grep -i block
dumpe2fs 1.41.12 (17-May-2010)
Block count:              1073741824
Reserved block count:     53687091
Free blocks:              1056843748
...

and 1073741824-1056843748 is 16898076 4k blocks, or 67592304 1k blocks
actually used.

If we ask for "minix df" by mounting with -o minixdf which is true blocks used, we get:

# df 4t-ext4/
Filesystem           1K-blocks      Used Available Use% Mounted on
/mnt/test2/mkfs-test/4tfile-ext4
                     4294967296  67592304 4012626628   2% /mnt/test2/mkfs-test/4t-ext4

I'd say this appears to be a slight inaccuracy in ext4_statfs, coupled with
the strangeness of the "bsd df" reporting.  It is apparently miscalculating
the filesystem metadata "overhead."

> I performed the same on XFS and the result was:
> 1TB: 32928
> 4TB: 32928
> 7TB: 33024

XFS is straightforward; blocks used for metadata count as "used."
Every other block is free and available.
No fiddling around, just like with the minixdf mount option for extN.

-Eric

> EXT4 result shows with increasing filesystem size, the number of used
> blocks decreased. I dont have idea about low level implementation but
> I am curious why it is so?
> 
> Thanks.
> 
> Regards,
> Adil
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: ext4: Used block count in df

[Adil Mujeeb]

Thanks Eric.

>> I have an observation on EXT4 filesystem. I created filesystem of size
>> 1TB, 4TB, and 7TB and then checked the output of df command.
>
> Telling us which version of e2fsprogs and which kernel would be helpful,
> but:

its 1.41.12.

> It reserves blocks for the superuser (5% by default) and also uses a lot
> of blocks up-front for filesytem metadata - inode tables, block bitmaps,
> and the like.

I also thinks so. But with this assumption, the number of 1KB blocks
used should increase as per filesystem size increase. No?

>
> But what you are seeing here is this:
>
> It also defaults to "bsd df" which does not count filesystem
> metadata when telling you about the number of blocks used.  So in theory,
> a freshly made fs should actually tell you 0 blocks used, I think.

Agree if "bsd df" assumes so.

> Looking at the dumpe2fs output for the 4t file, I see:
>
> # dumpe2fs -h 4tfile-ext4 | grep -i block
> dumpe2fs 1.41.12 (17-May-2010)
> Block count:              1073741824
> Reserved block count:     53687091
> Free blocks:              1056843748
> ...
>
> and 1073741824-1056843748 is 16898076 4k blocks, or 67592304 1k blocks
> actually used.
>
> If we ask for "minix df" by mounting with -o minixdf which is true blocks used, we get:
>
> # df 4t-ext4/
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /mnt/test2/mkfs-test/4tfile-ext4
>                      4294967296  67592304 4012626628   2% /mnt/test2/mkfs-test/4t-ext4
>
> I'd say this appears to be a slight inaccuracy in ext4_statfs, coupled with
> the strangeness of the "bsd df" reporting.  It is apparently miscalculating
> the filesystem metadata "overhead."

In your example, dumpe2fs and minix df both are reporting same value, isn't it?

I am still not able to understand why increasing the filesystem size
decreases used 1K block count :(
Am I missing some basic things here? Sorry if i am not able to catch
your point :(

Regards,
Adil

On Thu, Feb 7, 2013 at 10:19 PM, Eric Sandeen <sandeen@redhat.com> wrote:
> On 2/7/13 12:39 AM, Adil Mujeeb wrote:
>> Hi,
>>
>> I have an observation on EXT4 filesystem. I created filesystem of size
>> 1TB, 4TB, and 7TB and then checked the output of df command.
>
> Telling us which version of e2fsprogs and which kernel would be helpful,
> but:
>
>> df command showed the number of 1KB blocks used. The result was:
>> 1TB: 204056
>> 4TB: 198680
>> 7TB: 181784
>
> extN makes df complicated in several ways.
>
> It reserves blocks for the superuser (5% by default) and also uses a lot
> of blocks up-front for filesytem metadata - inode tables, block bitmaps,
> and the like.
>
> But what you are seeing here is this:
>
> It also defaults to "bsd df" which does not count filesystem
> metadata when telling you about the number of blocks used.  So in theory,
> a freshly made fs should actually tell you 0 blocks used, I think.
>
> Looking at the dumpe2fs output for the 4t file, I see:
>
> # dumpe2fs -h 4tfile-ext4 | grep -i block
> dumpe2fs 1.41.12 (17-May-2010)
> Block count:              1073741824
> Reserved block count:     53687091
> Free blocks:              1056843748
> ...
>
> and 1073741824-1056843748 is 16898076 4k blocks, or 67592304 1k blocks
> actually used.
>
> If we ask for "minix df" by mounting with -o minixdf which is true blocks used, we get:
>
> # df 4t-ext4/
> Filesystem           1K-blocks      Used Available Use% Mounted on
> /mnt/test2/mkfs-test/4tfile-ext4
>                      4294967296  67592304 4012626628   2% /mnt/test2/mkfs-test/4t-ext4
>
> I'd say this appears to be a slight inaccuracy in ext4_statfs, coupled with
> the strangeness of the "bsd df" reporting.  It is apparently miscalculating
> the filesystem metadata "overhead."
>
>> I performed the same on XFS and the result was:
>> 1TB: 32928
>> 4TB: 32928
>> 7TB: 33024
>
> XFS is straightforward; blocks used for metadata count as "used."
> Every other block is free and available.
> No fiddling around, just like with the minixdf mount option for extN.
>
> -Eric
>
>> EXT4 result shows with increasing filesystem size, the number of used
>> blocks decreased. I dont have idea about low level implementation but
>> I am curious why it is so?
>>
>> Thanks.
>>
>> Regards,
>> Adil
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>

Re: ext4: Used block count in df

[Eric Sandeen]

On 2/11/13 12:36 AM, Adil Mujeeb wrote:
> Thanks Eric.
> 
>>> I have an observation on EXT4 filesystem. I created filesystem of size
>>> 1TB, 4TB, and 7TB and then checked the output of df command.
>>
>> Telling us which version of e2fsprogs and which kernel would be helpful,
>> but:
> 
> its 1.41.12.
> 
>> It reserves blocks for the superuser (5% by default) and also uses a lot
>> of blocks up-front for filesytem metadata - inode tables, block bitmaps,
>> and the like.
> 
> I also thinks so. But with this assumption, the number of 1KB blocks
> used should increase as per filesystem size increase. No?
> 
>>
>> But what you are seeing here is this:
>>
>> It also defaults to "bsd df" which does not count filesystem
>> metadata when telling you about the number of blocks used.  So in theory,
>> a freshly made fs should actually tell you 0 blocks used, I think.
> 
> Agree if "bsd df" assumes so.
> 
>> Looking at the dumpe2fs output for the 4t file, I see:
>>
>> # dumpe2fs -h 4tfile-ext4 | grep -i block
>> dumpe2fs 1.41.12 (17-May-2010)
>> Block count:              1073741824
>> Reserved block count:     53687091
>> Free blocks:              1056843748
>> ...
>>
>> and 1073741824-1056843748 is 16898076 4k blocks, or 67592304 1k blocks
>> actually used.
>>
>> If we ask for "minix df" by mounting with -o minixdf which is true blocks used, we get:
>>
>> # df 4t-ext4/
>> Filesystem           1K-blocks      Used Available Use% Mounted on
>> /mnt/test2/mkfs-test/4tfile-ext4
>>                      4294967296  67592304 4012626628   2% /mnt/test2/mkfs-test/4t-ext4
>>
>> I'd say this appears to be a slight inaccuracy in ext4_statfs, coupled with
>> the strangeness of the "bsd df" reporting.  It is apparently miscalculating
>> the filesystem metadata "overhead."
> 
> In your example, dumpe2fs and minix df both are reporting same value, isn't it?
> 
> I am still not able to understand why increasing the filesystem size
> decreases used 1K block count :(
> Am I missing some basic things here? Sorry if i am not able to catch
> your point :(

My only point is, default ext4 statfs behavior is quite complicated, and it
looks like you have found a bug related to the calculation of metadata overhead.

It should only be a reporting issue, and should not cause any runtime issues.

Thanks,
-Eric
 
> Regards,
> Adil

Re: ext4: Used block count in df

[Eric Sandeen]

On 2/11/13 11:32 AM, Eric Sandeen wrote:
> On 2/11/13 12:36 AM, Adil Mujeeb wrote:
>> Thanks Eric.
>>
>>>> I have an observation on EXT4 filesystem. I created filesystem of size
>>>> 1TB, 4TB, and 7TB and then checked the output of df command.
>>>
>>> Telling us which version of e2fsprogs and which kernel would be helpful,
>>> but:
>>
>> its 1.41.12.
>>
>>> It reserves blocks for the superuser (5% by default) and also uses a lot
>>> of blocks up-front for filesytem metadata - inode tables, block bitmaps,
>>> and the like.
>>
>> I also thinks so. But with this assumption, the number of 1KB blocks
>> used should increase as per filesystem size increase. No?
>>
>>>
>>> But what you are seeing here is this:
>>>
>>> It also defaults to "bsd df" which does not count filesystem
>>> metadata when telling you about the number of blocks used.  So in theory,
>>> a freshly made fs should actually tell you 0 blocks used, I think.
>>
>> Agree if "bsd df" assumes so.
>>
>>> Looking at the dumpe2fs output for the 4t file, I see:
>>>
>>> # dumpe2fs -h 4tfile-ext4 | grep -i block
>>> dumpe2fs 1.41.12 (17-May-2010)
>>> Block count:              1073741824
>>> Reserved block count:     53687091
>>> Free blocks:              1056843748
>>> ...
>>>
>>> and 1073741824-1056843748 is 16898076 4k blocks, or 67592304 1k blocks
>>> actually used.
>>>
>>> If we ask for "minix df" by mounting with -o minixdf which is true blocks used, we get:
>>>
>>> # df 4t-ext4/
>>> Filesystem           1K-blocks      Used Available Use% Mounted on
>>> /mnt/test2/mkfs-test/4tfile-ext4
>>>                      4294967296  67592304 4012626628   2% /mnt/test2/mkfs-test/4t-ext4
>>>
>>> I'd say this appears to be a slight inaccuracy in ext4_statfs, coupled with
>>> the strangeness of the "bsd df" reporting.  It is apparently miscalculating
>>> the filesystem metadata "overhead."
>>
>> In your example, dumpe2fs and minix df both are reporting same value, isn't it?
>>
>> I am still not able to understand why increasing the filesystem size
>> decreases used 1K block count :(
>> Am I missing some basic things here? Sorry if i am not able to catch
>> your point :(
> 
> My only point is, default ext4 statfs behavior is quite complicated, and it
> looks like you have found a bug related to the calculation of metadata overhead.
> 
> It should only be a reporting issue, and should not cause any runtime issues.

For more info, take a look at fs/ext4/super.c:

/*
 * Note: calculating the overhead so we can be compatible with
 * historical BSD practice is quite difficult in the face of
 * clusters/bigalloc.  This is because multiple metadata blocks from
 * different block group can end up in the same allocation cluster.
 * Calculating the exact overhead in the face of clustered allocation
 * requires either O(all block bitmaps) in memory or O(number of block
 * groups**2) in time.  We will still calculate the superblock for
 * older file systems --- and if we come across with a bigalloc file
 * system with zero in s_overhead_clusters the estimate will be close to
 * correct especially for very large cluster sizes --- but for newer
 * file systems, it's better to calculate this figure once at mkfs
 * time, and store it in the superblock.  If the superblock value is
 * present (even for non-bigalloc file systems), we will use it.
 */
static int count_overhead(struct super_block *sb, ext4_group_t grp,
                          char *buf)

<much code ensues>

> Thanks,
> -Eric
>  
>> Regards,
>> Adil
> 
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: ext4: Used block count in df

[Adil Mujeeb]

Hi,

> My only point is, default ext4 statfs behavior is quite complicated, and it
> looks like you have found a bug related to the calculation of metadata overhead.

I see.
Where should I report this issue to get it confirm by developers?

> It should only be a reporting issue, and should not cause any runtime issues.

OK, I understand.

Thanks,
Adil

On Mon, Feb 11, 2013 at 11:02 PM, Eric Sandeen <sandeen@redhat.com> wrote:
> On 2/11/13 12:36 AM, Adil Mujeeb wrote:
>> Thanks Eric.
>>
>>>> I have an observation on EXT4 filesystem. I created filesystem of size
>>>> 1TB, 4TB, and 7TB and then checked the output of df command.
>>>
>>> Telling us which version of e2fsprogs and which kernel would be helpful,
>>> but:
>>
>> its 1.41.12.
>>
>>> It reserves blocks for the superuser (5% by default) and also uses a lot
>>> of blocks up-front for filesytem metadata - inode tables, block bitmaps,
>>> and the like.
>>
>> I also thinks so. But with this assumption, the number of 1KB blocks
>> used should increase as per filesystem size increase. No?
>>
>>>
>>> But what you are seeing here is this:
>>>
>>> It also defaults to "bsd df" which does not count filesystem
>>> metadata when telling you about the number of blocks used.  So in theory,
>>> a freshly made fs should actually tell you 0 blocks used, I think.
>>
>> Agree if "bsd df" assumes so.
>>
>>> Looking at the dumpe2fs output for the 4t file, I see:
>>>
>>> # dumpe2fs -h 4tfile-ext4 | grep -i block
>>> dumpe2fs 1.41.12 (17-May-2010)
>>> Block count:              1073741824
>>> Reserved block count:     53687091
>>> Free blocks:              1056843748
>>> ...
>>>
>>> and 1073741824-1056843748 is 16898076 4k blocks, or 67592304 1k blocks
>>> actually used.
>>>
>>> If we ask for "minix df" by mounting with -o minixdf which is true blocks used, we get:
>>>
>>> # df 4t-ext4/
>>> Filesystem           1K-blocks      Used Available Use% Mounted on
>>> /mnt/test2/mkfs-test/4tfile-ext4
>>>                      4294967296  67592304 4012626628   2% /mnt/test2/mkfs-test/4t-ext4
>>>
>>> I'd say this appears to be a slight inaccuracy in ext4_statfs, coupled with
>>> the strangeness of the "bsd df" reporting.  It is apparently miscalculating
>>> the filesystem metadata "overhead."
>>
>> In your example, dumpe2fs and minix df both are reporting same value, isn't it?
>>
>> I am still not able to understand why increasing the filesystem size
>> decreases used 1K block count :(
>> Am I missing some basic things here? Sorry if i am not able to catch
>> your point :(
>
> My only point is, default ext4 statfs behavior is quite complicated, and it
> looks like you have found a bug related to the calculation of metadata overhead.
>
> It should only be a reporting issue, and should not cause any runtime issues.
>
> Thanks,
> -Eric
>
>> Regards,
>> Adil
>
>

Re: ext4: Used block count in df

[Eric Sandeen]

On 2/12/13 12:14 AM, Adil Mujeeb wrote:
> Hi,
> 
>> My only point is, default ext4 statfs behavior is quite complicated, and it
>> looks like you have found a bug related to the calculation of metadata overhead.
> 
> I see.
> Where should I report this issue to get it confirm by developers?

Here is fine.  :)

It would be good to file a bug on bugzilla.kernel.org too if you like.

The problem is, I think ext4's metadata behavior has gotten so complex,
the consensus so far seems to be to just accept the inaccuracy in this
style of df reporting:

 * Note: calculating the overhead so we can be compatible with
 * historical BSD practice is quite difficult in the face of
 * clusters/bigalloc.  This is because multiple metadata blocks from
 * different block group can end up in the same allocation cluster.
 * Calculating the exact overhead in the face of clustered allocation
 * requires either O(all block bitmaps) in memory or O(number of block
 * groups**2) in time.  We will still calculate the superblock for
 * older file systems --- and if we come across with a bigalloc file
 * system with zero in s_overhead_clusters the estimate will be close to
 * correct ...

but it is odd behavior, and filing a bug would probably be good.

-Eric

>> It should only be a reporting issue, and should not cause any runtime issues.
> 
> OK, I understand.
> 
> Thanks,
> Adil
> 
> On Mon, Feb 11, 2013 at 11:02 PM, Eric Sandeen <sandeen@redhat.com> wrote:
>> On 2/11/13 12:36 AM, Adil Mujeeb wrote:
>>> Thanks Eric.
>>>
>>>>> I have an observation on EXT4 filesystem. I created filesystem of size
>>>>> 1TB, 4TB, and 7TB and then checked the output of df command.
>>>>
>>>> Telling us which version of e2fsprogs and which kernel would be helpful,
>>>> but:
>>>
>>> its 1.41.12.
>>>
>>>> It reserves blocks for the superuser (5% by default) and also uses a lot
>>>> of blocks up-front for filesytem metadata - inode tables, block bitmaps,
>>>> and the like.
>>>
>>> I also thinks so. But with this assumption, the number of 1KB blocks
>>> used should increase as per filesystem size increase. No?
>>>
>>>>
>>>> But what you are seeing here is this:
>>>>
>>>> It also defaults to "bsd df" which does not count filesystem
>>>> metadata when telling you about the number of blocks used.  So in theory,
>>>> a freshly made fs should actually tell you 0 blocks used, I think.
>>>
>>> Agree if "bsd df" assumes so.
>>>
>>>> Looking at the dumpe2fs output for the 4t file, I see:
>>>>
>>>> # dumpe2fs -h 4tfile-ext4 | grep -i block
>>>> dumpe2fs 1.41.12 (17-May-2010)
>>>> Block count:              1073741824
>>>> Reserved block count:     53687091
>>>> Free blocks:              1056843748
>>>> ...
>>>>
>>>> and 1073741824-1056843748 is 16898076 4k blocks, or 67592304 1k blocks
>>>> actually used.
>>>>
>>>> If we ask for "minix df" by mounting with -o minixdf which is true blocks used, we get:
>>>>
>>>> # df 4t-ext4/
>>>> Filesystem           1K-blocks      Used Available Use% Mounted on
>>>> /mnt/test2/mkfs-test/4tfile-ext4
>>>>                      4294967296  67592304 4012626628   2% /mnt/test2/mkfs-test/4t-ext4
>>>>
>>>> I'd say this appears to be a slight inaccuracy in ext4_statfs, coupled with
>>>> the strangeness of the "bsd df" reporting.  It is apparently miscalculating
>>>> the filesystem metadata "overhead."
>>>
>>> In your example, dumpe2fs and minix df both are reporting same value, isn't it?
>>>
>>> I am still not able to understand why increasing the filesystem size
>>> decreases used 1K block count :(
>>> Am I missing some basic things here? Sorry if i am not able to catch
>>> your point :(
>>
>> My only point is, default ext4 statfs behavior is quite complicated, and it
>> looks like you have found a bug related to the calculation of metadata overhead.
>>
>> It should only be a reporting issue, and should not cause any runtime issues.
>>
>> Thanks,
>> -Eric
>>
>>> Regards,
>>> Adil
>>
>>

Re: ext4: Used block count in df

[Adil Mujeeb]

Hi Eric,

On Tue, Feb 12, 2013 at 9:31 PM, Eric Sandeen <sandeen@redhat.com> wrote:
> On 2/12/13 12:14 AM, Adil Mujeeb wrote:
>> Hi,
>>
>>> My only point is, default ext4 statfs behavior is quite complicated, and it
>>> looks like you have found a bug related to the calculation of metadata overhead.
>>
>> I see.
>> Where should I report this issue to get it confirm by developers?
>
> Here is fine.  :)
>
> It would be good to file a bug on bugzilla.kernel.org too if you like.
>
> The problem is, I think ext4's metadata behavior has gotten so complex,
> the consensus so far seems to be to just accept the inaccuracy in this
> style of df reporting:
>
>  * Note: calculating the overhead so we can be compatible with
>  * historical BSD practice is quite difficult in the face of
>  * clusters/bigalloc.  This is because multiple metadata blocks from
>  * different block group can end up in the same allocation cluster.
>  * Calculating the exact overhead in the face of clustered allocation
>  * requires either O(all block bitmaps) in memory or O(number of block
>  * groups**2) in time.  We will still calculate the superblock for
>  * older file systems --- and if we come across with a bigalloc file
>  * system with zero in s_overhead_clusters the estimate will be close to
>  * correct ...
>
> but it is odd behavior, and filing a bug would probably be good.

I filed the bug in bugzilla. https://bugzilla.kernel.org/show_bug.cgi?id=53741
Thank for all your inputs :)

Regards,
Adil

>
> -Eric
>
>>> It should only be a reporting issue, and should not cause any runtime issues.
>>
>> OK, I understand.
>>
>> Thanks,
>> Adil
>>
>> On Mon, Feb 11, 2013 at 11:02 PM, Eric Sandeen <sandeen@redhat.com> wrote:
>>> On 2/11/13 12:36 AM, Adil Mujeeb wrote:
>>>> Thanks Eric.
>>>>
>>>>>> I have an observation on EXT4 filesystem. I created filesystem of size
>>>>>> 1TB, 4TB, and 7TB and then checked the output of df command.
>>>>>
>>>>> Telling us which version of e2fsprogs and which kernel would be helpful,
>>>>> but:
>>>>
>>>> its 1.41.12.
>>>>
>>>>> It reserves blocks for the superuser (5% by default) and also uses a lot
>>>>> of blocks up-front for filesytem metadata - inode tables, block bitmaps,
>>>>> and the like.
>>>>
>>>> I also thinks so. But with this assumption, the number of 1KB blocks
>>>> used should increase as per filesystem size increase. No?
>>>>
>>>>>
>>>>> But what you are seeing here is this:
>>>>>
>>>>> It also defaults to "bsd df" which does not count filesystem
>>>>> metadata when telling you about the number of blocks used.  So in theory,
>>>>> a freshly made fs should actually tell you 0 blocks used, I think.
>>>>
>>>> Agree if "bsd df" assumes so.
>>>>
>>>>> Looking at the dumpe2fs output for the 4t file, I see:
>>>>>
>>>>> # dumpe2fs -h 4tfile-ext4 | grep -i block
>>>>> dumpe2fs 1.41.12 (17-May-2010)
>>>>> Block count:              1073741824
>>>>> Reserved block count:     53687091
>>>>> Free blocks:              1056843748
>>>>> ...
>>>>>
>>>>> and 1073741824-1056843748 is 16898076 4k blocks, or 67592304 1k blocks
>>>>> actually used.
>>>>>
>>>>> If we ask for "minix df" by mounting with -o minixdf which is true blocks used, we get:
>>>>>
>>>>> # df 4t-ext4/
>>>>> Filesystem           1K-blocks      Used Available Use% Mounted on
>>>>> /mnt/test2/mkfs-test/4tfile-ext4
>>>>>                      4294967296  67592304 4012626628   2% /mnt/test2/mkfs-test/4t-ext4
>>>>>
>>>>> I'd say this appears to be a slight inaccuracy in ext4_statfs, coupled with
>>>>> the strangeness of the "bsd df" reporting.  It is apparently miscalculating
>>>>> the filesystem metadata "overhead."
>>>>
>>>> In your example, dumpe2fs and minix df both are reporting same value, isn't it?
>>>>
>>>> I am still not able to understand why increasing the filesystem size
>>>> decreases used 1K block count :(
>>>> Am I missing some basic things here? Sorry if i am not able to catch
>>>> your point :(
>>>
>>> My only point is, default ext4 statfs behavior is quite complicated, and it
>>> looks like you have found a bug related to the calculation of metadata overhead.
>>>
>>> It should only be a reporting issue, and should not cause any runtime issues.
>>>
>>> Thanks,
>>> -Eric
>>>
>>>> Regards,
>>>> Adil
>>>
>>>
>