tar command needs to add the "J" switch and XZ compression support
The GNU tar command has added the capital "J" switch for XZ (LZMA2) compression support.
illumos tar needs to incorporate this compression option and switch.
The 7z program can be called to perform the compression.
The optimized XZ compression algorithm provides the greatest level of compression, even better than bzip2 --best.
Although, it is much slower in execution.
The 7z SDK can be found here: http://www.7-zip.org/sdk.html
The GNU tar source can be found here: http://www.gnu.org/software/tar/
Additional XZ information can be found here: http://tukaani.org/xz/