Linux, politics, and other interesting things
Anthony Towns writes about using an improved version of jigdo to download CD/DVD images . His improvement is basically to pipeline operation for better performance.
Jigdo (the Jigsaw download) is a tool to download a set of files and then use them to create a CD or DVD image . The idea is that most web sites that have CD or DVD images also have a collection of files which comprise the DVD image available. This removes the need to store the data twice (wasting disk space on mirrors and in some situations breaking web caching).
I have never used jigdo, and for all Debian installations in recent times (the last few years at least) I download a small net-inst CD image and then have it download the other files from the net. I have Squid set up to cache large objects so this doesn’t waste too much of my precious network bandwidth (which is limited and expensive in Australia).
Now I’m thinking about what the optimum method for doing installs might be. One thing that would be good would be to support multiple repositories, the packages have unique file names and checksums so it should be possible to check one repository and then check another if it’s not working. I don’t mean multiple “deb” lines in the APT configuration. What I would like to do is to have an NFS file server or web server with an archive of downloaded packages and have APT check there first before downloading a file. So APT could get a list of packages from the net and then get the actual files locally if they are available.
The next thing that would be good is the ability to create a CD or DVD image dynamically and to store all temporary files. So I could download files from the repository and create a DVD image with just the packages that I need. Every time I create a DVD image my sub-set of the Debian archives would increase and the number of files actually downloaded in the creation process would be reduced. The effect would be to incrementally create a local mirror of the Debian repository.
Then I would like to see a two-stage DVD install process. I would like to boot from a CD or DVD and start the install and then have it give a list of files needed (which could be stored on a USB device or floppy) to create further CDs or DVDs for installation. One situation where this could have been beneficial was when I was doing an emergency install of CentOS. I did the first part of the install (selecting packages etc) to determine which CDs were needed. It turned out that almost all CDs were needed even though some of the CDs had only a few files that I was installing. If the installer could have written a list of packages to a USB device then I could have downloaded just those packages and got the install working a lot sooner. It seems to me that it’s fairly common to do one test install and then do some dozens of other installs with the same settings. So the ability to create a DVD of exactly the needed files for the other dozens of installs would be a great benefit.
Now this is just random commentary, unfortunately don’t have time to do any coding on this. But it seems obvious that something has to be done to improve the situation for developers and IT staff who need some degree of mirroring of the Debian package pool but who can’t do a full mirror. Back in 1996 I was able to mirror Debian over a 28K8 modem link and fit it on what was a reasonable hard drive by the standards of the day (incredibly tiny by today’s standards). Now I can’t practically mirror Debian over an Australian cable broadband connection and even by the standards of about 4 years ago (the age of most of my hard disks) the space requirements are significant.
I hope this post helps inspire some interest in developing these features. As delays in joining Debian  is the topic of the day it should be noted that work on preparing DVD images can easily be done by people who are not DDs. Such software should work from Debian archives without requiring any changes to them, and thus nothing special is needed from the Debian project to start work.