GNU bug report logs - #10561
stat unclear about size on disk and type of blocks discussed

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Message #19 received at 10561 <at> debbugs.gnu.org (full text, mbox):

From: Filipus Klutiero <chealer <at> gmail.com>
To: Pádraig Brady <P <at> draigBrady.com>
Cc: 10561 <at> debbugs.gnu.org, Jim Meyering <jim <at> meyering.net>
Subject: Re: bug#10561: stat unclear about size on disk and type of blocks
	discussed
Date: Fri, 20 Jan 2012 12:47:49 -0500

Hi Pádraig and Jim,

On 2012-01-20 09:15, Pádraig Brady wrote:
> On 01/20/2012 02:03 PM, Jim Meyering wrote:
>> Pádraig Brady wrote:
>> ...
>>>> As for %o, if you'd ask me what "I/O block size" means without any
>>>> context, I'm far from being sure I would answer it means size on
>>>> disk. I suggest to call this Size on disk, or Size used on the
>>>> filesystem.
>>> I/O implies transfer.
>>> So it corresponds to an "optimal transfer size hint"
>>> This value can be different at each layer, for example:
>>>
>>> $ stat -c "%o" .                # file level
>>> $ stat -f -c "%s" .             # file system level
>>> # blockdev --getioopt /dev/sda  # device level
>>>
>>>> I'm not sure what language should be used instead. Perhaps instead
>>>> of blocks the manual should talk about "data storage device blocks".
>>> I suppose we could clarify "I/O block size" a bit.
>>> How about s|I/O block size|optimal I/O block transfer size|
>> or even without "block",
>>
>>    "optimal I/O transfer size"
> OK I'll go with "optimal I/O transfer size hint",
> since there is nothing guaranteed about it,
> and in fact it's often wrong.
>
> cheers,
> Pádraig.
>

I'm sorry but this change does not really address my concern. The 
previous definition of %o did refer to "block" without specifying which 
kind of block. This is no longer the case as the new definition no 
longer refers to blocks. However, I still do not consider the new 
definition, "Optimal I/O transfer size hint", understandable.
To come back to my original problem, I tried figuring out how much disk 
space a small file took. In Windows, I would look at "Size on disk". If 
"optimal I/O transfer size hint" means size on disk, this is still very 
unclear. Even after reading your answers, I don't understand what 
"Optimal I/O transfer size" means. I am not looking for a transfer size. 
My question is, if I'm putting a small file on my filesystem, how much 
space will it use.
Here are 2 new descriptions I suggest:
Size occupied when including slack space
Size of the clusters occupied

Appart from %o, the ambiguity problem in the descriptions of %b and %B 
remains.

Thank you for the information about blocks and commands Pádraig.

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