GNU bug report logs -
#10561
stat unclear about size on disk and type of blocks discussed
Previous Next
Full log
Message #34 received at 10561 <at> debbugs.gnu.org (full text, mbox):
On 02/07/2012 06:26 PM, Filipus Klutiero wrote:
> Hi Pádraig,
>
> On 2012-01-20 19:03, Pádraig Brady wrote:
>> On 01/20/2012 05:47 PM, Filipus Klutiero wrote:
>>> 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.
>> It does actually, because...
>>
>>> 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.
>> ... you know to ignore %o
>
> What do you mean?
Above you realised you're not looking for a transfer size.
Hence it should be apparent that %o doesn't output anything
you're interested in.
>>
>>> 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.
>> No it does not.
>
> Really? The description of %b still reads:
>> Number of blocks allocated (see %B)
> How does this description exclude that it refers to file system blocks?
>
>> As I said they're abstract entities only valid in relation to each other.
>> Just multiple %b x %B to get your answer.
>
> If these statistics are internals, please mention that. It would also be nice to explain if the user can do anything with these internals.
I don't see any ambiguity. %b and %B are described in relation
to each other, which is all that's required.
See how each refers to the other in the docs:
%b Number of blocks allocated (see %B)
%B The size in bytes of each block reported by %b
>> You may have missed the start of the last mail, where I said
>> the du command is more appropriate (it does the above for you).
>>
>
> I did not miss that. I was looking for information from stat. I am not asking stat to provide that information. What annoyed me was that I couldn't tell if stat was providing that information because some of the statistics displayed were unclear.
> I'll try to remember to use du for that, thanks, but it's easier to remember a single command, and I generally prefer a command that tells me both the size on disk and the actual size.
The best we can do is:
stat -c 'allocated-space=%B*%b apparent-size=%s' $file
cheers,
Pádraig.
This bug report was last modified 13 years and 185 days ago.
Previous Next
GNU bug tracking system
Copyright (C) 1999 Darren O. Benham,
1997,2003 nCipher Corporation Ltd,
1994-97 Ian Jackson.