[Mageia-dev] Proposal for Mageia: implement bitorrent protocol to allow updates download

Wed Jan 12 15:10:52 CET 2011

Olivier Thauvin a écrit :
+> * andre999 (andr55 at laposte.net) wrote:
+>> Michael Scherer a écrit :
+>>>
+>>> Le mardi 11 janvier 2011 à 20:03 +0100, Marcello Anni a écrit :
+>>
+>> In my case, using aria2c with 2 mirrors and the default 5 connexions is
+>> at least 3 times as fast as a single connexion (to my closest mirror).
+>> And a much greater improvement over other download options I've tried.
+>
+> This is a selfish point of view, nothing is important except the result
+> on your side.
+
+Sorry, but this can't be serious.
+If a user is to download say a 4,7G DVD iso, it is 4,7G if the user uses 
+one or 5 connexions, from one or 5 mirrors.
+And if the 5 connexions go to 5 different mirrors, that is only 20% per 
+mirror.
+Globally, if the same files are downloaded, the same amount of data is 
+downloaded.
+What we are talking about here, from the user side, is downloading 
+faster, if the capacity is _available_ on the network of mirrors.
+Nothing more, nothing less.
+
+There are many mirrors which provide multiple connexions, with a very 
+large bandwidth.  If users don't use the available connexions on these 
+servers, other mirrors will be more heavily impacted.
+So, as I said in another post on this thread, it is win-win for both 
+users and mirrors.
+
+> But as I can see the results of such thing on distrib-coffee I can tell:
+> - often the bandwidth limititation is client side (eg you, with your DSL
+>    connection, and not the mirror, with 100mbits/s or more)
+> - all mirrors have limit, and when the max connection will be reached
+>    the mirror will stop serving you (download will be very faster !)
+
+That is the advantage of applications like aria2c.  They search 
+available connexions from the urls (mirrors) given, and choose which 
+give the fastest downloads.  The number of connexions vary according to 
+the conditions.  With the default of 5 connexions, aria2c tries to 
+maintain 5 connexions, but in practice fluctuates (dynamically) between 
+3 and 5, according to conditions.  (From my experience.)
+
+Think of it another way.
+Scenerio 1)  Suppose at this moment the mirror network has 20% free 
+capacity.  We download without multiple connections or multiple mirrors, 
+without using this excess capacity.  In one hour we are still 
+downloading, at a time when there is no free capacity.
+
+Scenerio 2) We download using multiple connexions and multiple mirrors, 
+accelerating the downloads with the otherwise unused 20% free capacity. 
+  In one hour, most of our downloads are finished, thus leaving free 
+capacity.
+
+Just who is served by scenerio 1 ?
+The users that don't have access, or the mirrors that are overloaded ?
+
+> Of course, if in the case I don't blacklist mageia and deny download via
+> http/ftp to save my mirror (d-c is already under heavy load).
+>
+> So, no, don't donwload several times from a mirror.
+
+The solution ?  If a mirror can't handle multiple connexions, restrict 
+it in some way.  Many mirrors do.  Either all the time, or from time to 
+time.  Or throttle the transfer speed.
+Just do whatever works best for the mirror in question.
+However let users use the capacity available.  Because it may not be 
+available in one hour, or even 5 minutes.
+
+> BTW: on distrib-coffee bandwidth is regulated by IP, not connection,
+> downloading 5 times will not be faster than 1.
+
+Essentially the same thing.  Great, if it works for the mirror.
+
+aria2c senses the the bandwidth dynamically, and reacts accordingly. 
+I'm sure that many other applications do the same thing.
+Don't forget that much of the increase in download speed comes from 
+using multiple mirrors. (Clearly indicated in the aria2c documentation, 
+and verified in my usage.)
+
+Why not think globally ?
+
+another 2 cents :)
+
+-- 
+André
+