[Fedora-livecd-list] [PATCH] cleanupDeleted and container_size - saves 5.5% output size on f7livecd-i686

[Phillip Lougher]

Douglas McClendon-2 wrote:
> 
> Douglas McClendon wrote:
> 
> Ok, so there is a negative consequence of a large container.  As I alluded
> to 
> before, mksquashfs apparently does not give any special consideration to
> sparse 
> files.  Naturally it can compress a file containing huge blocks of 0s
> pretty 
> well, but it still appears to be going to an aweful lot of work to do
> that.
> 
> Short of adding more intelligent handling of sparse files to squashfs 
> (feasible?), another alternative which satisfies the above resizing
> scenarios 
> would be this-
> 

Unfortunately, I have been aware for sometime that the Fedora liveCD uses
sparse files, and Squashfs support was lacking.  Happily Squashfs now has
sparse file support (in CVS).  Max block size has also been increased from
64K to 1Mbyte, with the default 128 Kbytes.

Some stats based on the Fedora-8-Test-1-Live-i686.iso 

original squashfs.img 712495104 (681M)
sparse squashfs.img 709820416 (678M)
sparse squashfs.img with 128Kbyte blocks 700100608 (669M)

So, the compressed 0s used to take up about 2.5 Mbytes.  More significant is
the data and seek time saving in not reading all these useless compressed
0s.

time to do "dd if=os.img of=/dev/null" from CDROM

original squashfs.img, 221 seconds
sparse squashfs.img, 168 seconds
sparse squashfs.img with 128byte blocks, 171 seconds

on average about 20% speedup.

Regards

Phillip



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