gistfile1.txt

File:
CentOS 5.7 i386 20GB (gzipped -> 649MB)

use File::Copy;
copy($baseImageFileName, $imageFileName);

real    6m34.418s
user    0m0.394s
sys     0m47.059s

use IO::Uncompress::Gunzip qw(gunzip $GunzipError);
gunzip $baseImageFileName => $imageFileName or die "gunzip failed: $GunzipError\n";

real    8m6.076s
user    7m8.536s
sys     0m52.057s

system("zcat $baseImageFileName | cp --sparse=always /dev/stdin $imageFileName");

real    1m58.766s
user    1m51.205s
sys     0m12.642s

system("cp --sparse=always $baseImageFileName $imageFileName");

real    0m52.733s
user    0m1.832s
sys     0m21.427s