Re: [CAD_CAM_EDM_DRO] Sneakernet

At 20:27 04/04/2001 +0000, you wrote:

> > Actually, with a few DAT tapes in your pocket, you can achieve MUCH higher
> > data transfer rates with sneakernet than with 100 Mbit/s Ethernet.
>
>Absolute baloney! I have only 10 MB/S ethernet, and I can transmit
>the full EMC ditribution set in less than 5 seconds. So, that is close to
>1 MBYTE / second. Given the time to write a tape, carry it, and read
>it at the other location, I'm sure that even the 10MB/sec ethernet is
>a little faster. The 100 MB/sec is WAY faster, it should transfer at
>nearly 100% of the transfer rate of the slowest hard disk drive.
>Note that with the net, you are reading from one computer and writing
>on the other SIMULTANEOUSLY.

Very far from being absolute baloney, actually. The point is that when you
are talking about transferring very large volumes of data, the speed of the
network becomes less important relative to the speed of accessing it
from/writing it to backing storage devices, and even the speed at which you
can transfer data between the network interface and the computer's RAM can
become a major limiting factor.

If you are shipping a significant amount of data (i.e., more than you can
accommodate in RAM on the source or destination machines - lets say more
than 100 megabytes, for the sake of argument - not unreasonable for a
well-specced PC with 256 megs of RAM - you gotta leave some room for
Windoze <G>), then the data transfer rate between the two machines is
absolutely limited by the rate at which you can get the data off the source
machine's backing storage (which we will assume is the same rate at which
the target machine can write to its backing storage). However fast the
network is, once you've shipped the first 100 megs, you're down to the
speed of the disk/floppy/tape etc. accesses - the data has to be somewhere,
and it ain't in RAM.

Given that the stuff must already be available on a disk (or cartridge,
tape, floppy...etc), in the source machine, it can indeed be quicker to
simply unplug the disk (or cartridge, tape, floppy...etc) from the source
machine & plug it into the destination machine. That way, the data is
immediately available to the target machine, without the delays imposed by
reading, transferring across the net and writing.

Its not unusual to have removable hard drives on computers these days - I
have 2Gigabyte Jazz drives on my machines, for example. Using your 10
Mbit/S Ethernet network, and your transfer rate of a megabyte/second (which
is close to the maximum you can achieve on 10 Mbit/s Ethernet), it would
take me 2000 seconds - a little over half an hour - to transfer the
contents of one Jazz cartridge over the LAN. Even with 100 Mbit/s Ethernet
(which I have on my home/workshop LAN), and assuming that a Windows machine
can actually use the full 100 Mbit/s available on a continuous basis, while
simultaneously doing bulk disk accesses (which I seriously doubt, by the
way), and ignoring the access speed of the Jazz drive (a relatively slow
hard drive), we're talking 3 minutes to ship the contents of a 2 Gig Jazz
cartridge from machine to machine on my network. I absolutely guarantee
that I can unplug the cartridge, walk to any other machine on my network,
and plug the cartridge in in less than 3 minutes. 30 seconds tops.

With removable hard drives (or DAT tapes, as in my original comment) of,
say, 40 Gigabytes capacity, the data transfer rates you can achieve with
sneakernet become really quite high - equivalent to a data rate of 640
gigabits per second if you can unplug/replug the drive or tape within 30
seconds. Even the leading edge LAN technologies only manage 10
Gigabits/second right now.

Regards,
Tony