[bittorrent] IO bound

Carsten Otto c-otto at gmx.de
Thu Apr 12 13:11:24 EDT 2007

On Thu, Apr 12, 2007 at 07:05:00PM +0200, Joris Guisson wrote:
> Ramdisk maybe ? Create a ramdisk and copy the data in there, then
> import with your preferred client. That way there is no disk involved
> at all, and your biggest bottleneck is gone.

There is no need for a RAM disk, as the client could load everything
into the RAM or the operating system could cache file accesses.
The problem is the size of the torrent. A DVD image with about 5 GByte
does not fit into the RAM of my systems. Seeding a CD image with about
700 MByte is no problem. Because of this the torrents for the Debian CD
images are very slow (for me as an uploader), because other peers
already served the clients (besides, the download is smaller). There is
no need to serve small files with high speed, a lot of clients already
do that :)

> Euhm, why would HAVE messages have any impact upon which chunks are
> loaded into RAM ?

I'd modify/create/... the client such that the HAVE messages only
contains chunks that are loaded.
1) Randomly (?) load chunks until the RAM is full
2) send HAVE message with _only_ these chunks
3) Based on some criteria free the RAM and start at 1)

> Most clients probably download the rarest chunks first, those might be
> the ones you want to keep into memory.

My operating system (and client) does that automatically. It does not
work as you think. With one Debian DVD image and 1,5 GByte of RAM
reserved for utorrent I am still bound by the disk speed.

Carsten Otto
c-otto at gmx.de
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