Re: Inefficient storing of ISO images with compress=lzo

[Li Zefan <lizf@xxxxxxxxxxxxxx>]

07:06, Maciej Marcin Piechotka wrote:
> On Mon, 2011-09-19 at 10:53 +0800, Li Zefan wrote:
>> Maciej Marcin Piechotka wrote:
>>> I've noticed that:
>>>
>>>  - with x86-64 Fedora 15 DVD install images:
>>>    - du -sh <ROOT VOLUME> was 36 GB
>>>    - btrfs df | grep -i data have shown over 40 GB used
>>>  - without
>>>    - du -sh <ROOT VOLUME> is 34 GB
>>>    - btrfs df | grep -i data have shown less then 34 GB used
>>>
>>> It seems that iso files are considered compressable while they may not be (and penalty is severe - 3x).
>>>
>>
>> With compress option specified, btrfs will try to compress the file, at most
>> 128K at one time, and if the compressed result is not smaller, the file will
>> be marked as uncompressable.
>>
>> I just tried with Fedora-14-i386-DVD.iso, and the first 896K is compressed,
>> with a compress ratio about 71.7%, and the remaining data is not compressed.
>>
>> --
>> Li Zefan
> 
> Just a question from person who don't know how btrfs operates - what if
> the beginning of file is well compressable and the rest is not?
> 

It's explained in the previous mail - the beginning part will be compressed,
and the rest will not.

> In any case the compression was my uneducated guess where is missing
> 4GB.
> 

It probably has nothing to do with compression. You can try without compress=lzo,
and see if the issue still exists.
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