dd as an imaging solution.
gurney_j at resnet.uoregon.edu
Fri Feb 9 23:18:33 UTC 2007
Sean Bryant wrote this message on Fri, Feb 09, 2007 at 14:07 -0500:
> John-Mark Gurney wrote:
> >Antony Mawer wrote this message on Tue, Feb 06, 2007 at 17:04 +1100:
> >>On 6/02/2007 1:47 PM, Sean Bryant wrote:
> >>>Dominic Marks wrote:
> >>>>Check out G4U (NetBSD based)
> >>>The only problem I can see here is that multiple parallel reads will
> >>>have serious performance impacts, thus greatly increasing the cloning of
> >>>the disk.
> >>>The solution with dd, tee and netcat would just daisy chain the copy
> >>>across the network which would be way faster.
> >>Now all you need is G4U to operate in a multicast manner like Symantec
> >>Ghost Corporate Edition, and your transfer speed wouldn't reduce with
> >>each additional client (eg. 100mbps for 1 client, 50mbps each for 2
> >>clients, 33.3mbps each for 3 clients, ...)
> >Add FEC to the multicast, and you can constantly stream the data, and
> >not have to worry about dropped segments as much...
> Can you explain this?
FEC stands for Forward Error Correction... Check out:
for some work that Luigi has done wrt FEC. I've even embedded his FEC
library in the kernel w/o too much difficulty... Wikipedia also has
an article on it...
So the idea is that you multicast out the data broken up into x packets..
In addition to x packets, you also transmit y "parity" packets... As
long as the end system receives any combination of x and y packets where
the total unique packet count is x, you are able to reconstruct the
You choose y based upon your expected packet drop rate.. This has the
advantage that when you are transmitting the data, and a machine fails
to receive a packet, you don't have to a) retrainsmit the packet, or
b) wait till the same data packet comes along... Because you can
replace the missed data packet w/ one of the parity packets to reconstruct
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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