[Udpcast] what is the speed bottleneck?

[Donald Teed]

I think Alain provided an excellent tip on how to deal
with the megabit ethernet.  However I just want to
add that in my experience the target client disk drive
is always the bottleneck.  It really depends on what you
are imaging and whether compression is used.

Remember that the transfer rate is showing the packets
transfer rate, and not the rate being written to the disk.

We use a 100 Mbit network to image 40 GB client notebook
drives.  Given that most of the drive on the master
machine has been zero'ed, it compresses very well to
less than 3GB of image.  When we send out the image
to the client notebooks, the sender machine disconnects
from all clients, and the clients remain writing
data (mostly highly compressed zeros) to disk from their
512 MB available RAM for the next 4 or 5 minutes,
which covers about 5 or 6 GB of client disk writing.

The only way I can imagine the network being a bottleneck
is if:
- the network is already saturated with other traffic
- the image is not created as compressed
- the master disk is nearly full
- the master disk is not zeroed in the empty sectors

--Donald Teed


On Thu, 23 Sep 2004, Ramon Bastiaans wrote:

> Hi all,
>
> I was wondering if anyone knows or could tell what the bottleneck is for
> udpcast multicast speeds?
>
> We have been using udpcast satisfactory for a while now in combination
> with systemimager. In our previous situation the maximum speed seemed to
> be around 20 Mbps (MAX_BITRATE). Setting the speed any higher would
> result in dropped slices in the cast and some receivers not getting the
> image in the first cast. This was on a 100 Mbps network.
>
> We now have a new setup where we image machines over a 1000 Mbps
> network, and the maximum speed seems to be 40 Mbps for udpcast? If we
> cast any faster the number of machines failing to successfully receive
> the cast dramatically increases (even though in the first tests, even at
> 40 Mbps there are 3 out of 40 still dropping).
>
> Now this is on machines with 15.000 rpm scsi disk's. The hd and network
> both should be able to go as fast as 100 MByte/sec in theory. However we
> can't even get a stable cast at a 10th of this speed. It's not a very
> big issue since we save a lot of time by imaging all machines at the
> same time, but I was still wondering what exactly the bottleneck for the
> multicast's speed is.
>
> Is it the udp protocol, or the multicast technique, or could it still be
> a hardware issue?
>
> Any opinions on the subject are appreciated, perhaps some of the authors
> of udpcast could give some insight?
>
> Kind regards,
>
> --
> Ramon Bastiaans
> SARA - Academic Computing Services
> Kruislaan 415
> 1098 SJ Amsterdam
>
>
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