how to create file without using extent allocation

[Greg Freemyer]

> On 3/22/12, Vlad Dogaru <ddvlad at rosedu.org> wrote:
>> On Thu, Mar 22, 2012 at 3:31 PM, Akshay Nehe <akshaynehe785 at gmail.com>
>> wrote:
>>> Hello,
>>>
>>> Can we create file on ext4 file system which dose not uses extent
>>> allocation?
>>
>> Man page of mkfs.ext4 suggests using "-O ^feature" to disable an ext4
>> feature.  This seems to work:
>>
>> $ dd if=/dev/zero of=test1 bs=4M count=20
>> [...]
>> $ mkfs.ext4 -F test1
>> [...]
>> $ file test1
>> test1: Linux rev 1.0 ext4 filesystem data,
>> UUID=408f6da2-c4ef-4335-9574-985f3a349ed2 (extents) (huge files)
>>
>> $ mkfs -O ^extent -F test1
>> [...]
>> $ file test1
>> test1: Linux rev 1.0 ext4 filesystem data,
>> UUID=23c046d6-db7a-419d-a1d5-0cba3c5b52d0 (huge files)
>>
>> Hope this helps,
>> Vlad
>>


On Thu, Mar 22, 2012 at 9:59 AM, Akshay Nehe <akshaynehe785 at gmail.com> wrote:
> Thanks for help, i find it useful.
>
> --
> Regards,
> Akshay Nehe.

Akshay,

1) If you are going to participate in kernel mailinglists, you need to
be aware the appropriate netiquette is to bottom post all responses.
I have moved your reply to the bottom to make this flow better.

2) I assume you see it is a mkfs option that controls this.  So you
can't control it on a file by file basis as far as I know.  I don't
think you can even control it by re-mounting.  Instead you have to
reformat, so it is a fundamental change.

Greg