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Jigdo vs. BitTorrent vs. normal downloads [was: Re: portability of jigdo]



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On Du, 31 aug 14, 18:36:42, Rusi Mody wrote:
> Context:
> On the tex user group, someone was asking/complaining about the difficulties of downloading texlive.
> 
> - One has to download one (few?) large (in GBs) dvd image
> - The user was on a slow/flaky line
> 
> In response the texlive folks admitted that there was a problem without 
> a clear solution.
> 
> It occurred to me that jigdo is made for exactly this kind of issue.

No, it is meant to decrease load and/or space on the servers hosting ISO 
files.

> So the question, how easy is it to port jigdo?
> 
> Two parts to the question:
> 
> 1. Jigdo server can presumably be run on a unix system, specifically 
> debian. So the 'porting' required is not much more than changing the files
> served from debian-installers to texlive-installers

There's no such thing as a jigdo "server", see below.

> 2. Jigdo client should run on all OSes (including windows)
 
It does.

> Looking around the docs I find that the easier part (1) is undocumented (or I didn't find any)

There is no part 1. Jigdo relies on the fact that Debian ISOs contain 
mostly just .deb files. Those .deb files are *also* available from the 
regular package mirrors, which are plenty and might have better 
connectivity to you.

Jigdo takes a template file (the ISO "skeleton" without all the .deb 
files in it) and then adds the .deb files to it. The nice thing about 
jigdo is that it can use .deb files from whatever source:

- other ISO images
- your /var/cache/apt/archives
- Debian mirrors

Because of this one can use jigdo to create ISOs for a new point release 
by using ISO files from a previous point release and just a few 
additional downloads. It won't work so well between stable releases 
because most packages are updated.

Jigdo is also used to "host" ISOs that are used less often (e.g. other 
architectures, BD images, etc.), because one only has to provide the 
template files, all the .debs are already on the mirrors.

This is not possible with BitTorrent because there has to exist at least 
one full copy (usually the initial seed) in the torrent.

If the bottle-neck is the internet connection at home neither technology 
will help, because jigdo, BitTorrent and normal downloads (FTP/HTTP) 
need to download the same amount of data. BitTorrent could be worse than 
the others because it also uploads data.

If the bottle-neck is at the server both jigdo and BitTorrent can help, 
but only provided there exist alternative download sources. Jigdo uses 
other servers hosting files contained in the ISO while BitTorrent uses 
pieces of the ISO already downloaded by other clients.

Kind regards,
Andrei
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