Incorrect file size?

[Krassimir Slavchev]

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Oliver Fromme wrote:
> Ivan Voras wrote:
>  > Rink Springer wrote:
>  > > The 'vscan' user leads me assume this is SpamAssassin - I've seen this
>  > > behaviour at work, where our scripts were trying to backup a 1TB file
>  > > (which actually was ~vscan/.spamassassin/auto-whitelist). The result was
>  > > that the backup script died due to lack of disk space on the backup
>  > > server (as we don't use compression).
>  > > 
>  > > When I was investigating why the file could be so large it, it turned
>  > > out the file was only a few hunderd 'real' MB's, so that is why I assume
>  > > this person is having the same issue as we do. The file is a Berkeley DB
>  > > file, by the way, so there's nothing textfile about it ;-)
>  > 
>  > I learn something every day :)
>  > Didn't know BDB was smart enough to create sparse files.
> 
> BTW, you can use "ls -ls" to display the number of physical
> blocks allocated to the file, so you can easily see whether
> a file is sparse or not:
> 
> $ dd if=/dev/zero of=foo1 bs=1m count=1
> $ truncate -s 1m foo2
> $ ls -ls foo1 foo2
> 1040 -rw-------  1 olli  olli  1048576 Jun 20 22:43 foo1
>   32 -rw-------  1 olli  olli  1048576 Jun 20 22:43 foo2

# ls -lsk
total 1247288
 664064 -rw-------  1 vscan  vscan  4398199488512 Jun 23 09:39
auto-whitelist
     88 -rw-------  1 vscan  vscan          89976 Jun 23 09:39 bayes_journal
 566704 -rw-------  1 vscan  vscan  1099639861248 Jun 23 09:39 bayes_seen
  16432 -rw-------  1 vscan  vscan       21454848 Jun 23 09:39 bayes_toks

> 
> As you can see, the file size is the same, but the block
> counts are different (I have BLOCKSIZE=K in my environment,
> so the blocks are displayed in 1KB units).
> 
> I've written a small script that can be used to detect
> sparse files (it even displays the "sparseness" percentage):
> 
> http://www.secnetix.de/olli/scripts/sparsecheck
> 
> Best regards
>    Oliver
> 
> PS:  Of course it is still possible that a file system is
> corrupt and needs fsck, no matter whether those files are
> sparse or not.
> 


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