Re: [Xen-users] Live DemoCD / cow? storage

["Fernando Maior" <fernando@xxxxxxxxxxxxx>]

> I don't understant what is the 'cow' setting?
> CU,
>     Antoine N.

Antoine,

COW is an acronym for Copy On Write.

For booting and running an Operating System, you
need a lot of files installed into a partition.
If you copy that partition to a file, you have a
root partition image.

And, if you want to use a number of Xen domains,
but your disk space is not enough for the needed
root partitions (one for each domain), you can
use COW.

Just install one only partition, make a root
partition image from that to a file, and set
it read-only. Now you can set the domain to
use it WITH a second file, a COW file, that
will be created and mantained by the kernel
as a sparse file. Everything you write to the
root partition will go, instead, to the COW
file. For example, configuration files in the
/etc directory.

They are really useful, I have a configuration
with one host machine with 8 UML virtual machines
inside, all of them using only one root partition
image, each of them having their exclusive cow file.

Yet, I do not know how to use them from Xen. If you
are interested, go ahead and ask.

-- 
Bye,
Fernando Maciel Souto Maior
fernando@xxxxxxxxxxxxx
http://www.araujo.com.br
+55+31 3270-5886
LPIC/1 # 31908

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