AW: AW: [Xen-users] Understanding sparse-files

["Rustedt, Florian" <Florian.Rustedt@xxxxxxxxxxx>]

 Oh, sh.t ;)

Well, no big clue to see that, if the real size is zero!
I hope, i'll think a little deeper next time i am asking, thanks again for your 
time spent to answer.

Kind regards, Florian

> -----Ursprüngliche Nachricht-----
> Von: John Haxby [mailto:john.haxby@xxxxxxxxxx] 
> Gesendet: Dienstag, 16. Dezember 2008 16:14
> An: Rustedt, Florian
> Cc: xen-users@xxxxxxxxxxxxxxxxxxx
> Betreff: Re: AW: [Xen-users] Understanding sparse-files
> 
> Rustedt, Florian wrote:
> >  Thank you!
> >
> > That was exactly what i needed ;)
> >
> >   
> 
> My pleasure.
> 
> > Does the choosen blocksize has impact on the formatting, so 
> do i need to take smaller blocksizes if i want to use the 
> space with the filesystem i am choosing more efficiently?
> > Or is it just for calculation, so formatting a "dd bs=512K 
> seek=2048" results exactly in the same filesystemlayout after 
> formatting as a "dd bs=1M seek=1024" would do?
> > So in both cases, i can use a "mkfs.ext2 -b 512 huge" and 
> the resulting file mounts in both cases equally with a 256 
> Byte blocksize?
> >   
> 
> Files don't have block sizes :-)   dd just multiples the 
> block size and 
> seek to find the starting offset.  In fact, as the count is 
> zero (write nothing at all to the file), dd bs=1M seek=20480 
> count=0 turns into this:
> 
>     open("/dev/zero", O_RDONLY)             = 3
>     dup2(3, 0)                              = 0
>     close(3)                                = 0
>     lseek(0, 0, SEEK_CUR)                   = 0
>     open("huge", O_RDWR|O_CREAT, 0666)      = 3
>     dup2(3, 1)                              = 1
>     close(3)                                = 0
>     ftruncate(1, 21474836480)               = 0
> 
> The important call is the last one.
> 
> jch
> 
> 
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