Re: something magic about the size of a ports tree

On 2023-10-03 12:24, Dag-Erling Smørgrav wrote:
> Matthias Apitz <guru@unixarea.de> writes:
>> I have on my poudriere build host a ports tree and wanted to move it to
>> the host where the resulting packages are installed:
>>
>> root@jet:/usr/local/poudriere/ports # du -sh ports20230806
>> 397M    ports20230806
>> root@jet:/usr/local/poudriere/ports # tar cf p.tar ports20230806
>> root@jet:/usr/local/poudriere/ports # ls -lh p.tar
>> -rw-r--r--  1 root wheel  672M Oct  3 18:00 p.tar
>>
>> already the size of the tar file is somewhat magic; but if you un-tar it
>> on the other host I will get:
>>
>> [guru@c720-1400094 ~]$ ls -lh p.tar
>> -rw-r--r--  1 guru wheel  672M  3 oct.  18:00 p.tar
>> [guru@c720-1400094 ~]$ tar xf p.tar
>> [guru@c720-1400094 ~]$ du -sh ports20230806
>> 1,2G	ports20230806
>>
>> How this is possible?
> 
> Most files in the ports tree are very small.  On disk, each file gets
> rounded up to the nearest multiple of the filesystem block size, which
> could be as small as 512 bytes or as large as 8 kB (or even more in
> pathological cases).  In a tarball, they get rounded up to the nearest
> multiple of 512 bytes plus an additional 512 bytes per file for
> metadata.
> 
> For instance, your average distinfo file (of which there are 30k in the
> ports tree) is only 200-250 bytes long, but it occupies 512 bytes on an
> FFS filesystem, 1 kB in a tarball, and 4 kB on a typical ZFS filesystem.
> 

As an interesting side note to this, if ZFS is able to compress the file 
to under 112 bytes, ZFS will not allocate a sector, but instead store 
the file in an "embedded blockpointer", basically using the space it 
would normally store the LBAs and checksum of the file, to store the 
actual file data, resulting in a file that appears to use 0 bytes of 
space, because it entirely fits in the indirect block that would have 
pointed to the block itself.

> Note that if the target system is FreeBSD 14 or newer, you can simply
> mount the tarball (`sudo mount -rt tarfs p.tar /usr/ports`).
> 
> DES



-- 
Allan Jude