Month: February 2014

A few words on lzip compressor

(update on 2016-01-28: please note that this post is outdated and no longer adequately expresses my attitude towards the two competing formats)

Some of you may already have noticed that sys-apps/ed and sys-fs/ddrescue packages started pulling in lzip archiver. «Is this some new fancy archiver?» you may ask. The answer is «no. It’s been around for a very long time, and it never got any real interest.»

You can read some of the background story in New Options in the World of File Compression Linux Gazette article. Long story short, lzip was created before xz as a response to the limitations of .lzma format used by lzma-utils. However, it never got any real attention and when xz-utils was released as a direct successor to lzma-utils it became practically redundant. And the two projects co-existed silently until lately…

Over the past five years, Antonio Diaz Diaz, lzip’s author, and a few project supporters were trying to convince the community that the lzip format is superior to xz. However, they were never able to provide any convincing arguments to the community, and while xz gained popularity lzip stayed in the shadow. And it was used mostly by the projects Diaz was member of.

It seems that he has finally decided that advocacy will not help his pet project in gaining popularity. Instead, he decided to take advantage of his administrator position in the mentioned GNU projects and discontinue providing non-.lz tarballs. As he says, «surely every user of ddrescue would like to know about lzip […]».

So, Gentoo user, would you like to know about lzip? Let’s try to get a few fair points here.

Continue reading “A few words on lzip compressor”

Using deltas to speed up SquashFS updates

The ebuild repository format that is used by Gentoo generally fits well in the developer and power user work flow. It has a simple design that makes reading, modifying and adding ebuilds easy. However, the large number of separate small files with many similarities do not make it very space efficient and often impacts performance. The update (rsync) mechanism is relatively slow compared to distributions like Arch Linux, and is only moderately bandwidth efficient.

There were various attempts at solving at least some of those issues. Various filesystems were used in order to reduce the space consumption and improve performance. Delta updates were introduced through the emerge-delta-webrsync tool to save bandwidth. Sadly, those solutions usually introduce other inconveniences.

Using a separate filesystem for the repositories involves additional maintenance. Using a read-only filesystem makes updates time-consuming. Similarly, the delta update mechanism — while saving bandwidth — usually takes more time than plain rsync update.

In this article, the author proposes a new solution that aims both to save disk space and reduce update time significantly, bringing Gentoo closer to the features of binary distributions. The ultimate goal of this project would be to make it possible to use the package manager efficiently without having to perform additional administrative tasks such as designating an extra partition.

Read on… [PDF]