foo@xxxxxxxxx wrote:
I have a need to create a CoW (copy on write) on the root filesystem using
device mapper. I do this manually after installation. I'd like to see
this type of setup integrated into anaconda.
Although I have a specific need, I see many other possible applications
for CoWs that could use this type of feature.
o Embedded flash devices with persistence that are easy to clear or reset.
o Stateless installations where the CoW(s) are cleared at reboot or logout.
o Testing installations where you may have several CoWs for for testing a
single base installation that are easy to cleared or reset.
o Virtual installations that using the same root filesystem with
modifications by the different instances saved in different CoWs
I would like to see this handled in the anaconda partition setup where you
could define a partition as a CoW for one of the mounted filesystems. Add
a kernel parameter similar to the “root=” except something like “cow=” to
define a root filesystem CoW and have a similar file as “fstab” except
maybe “cowtab” that defines non-root filesystem CoWs and where they are
located.
I think you may even have more ideas. I think even the LiveCDs that use
device mapper with an in-memory CoW due to the read-only CD media would
benefit from anaconda support (add a kernel parameter something like
“cow=RAM=100mb”.
Am I crazy or alone in my needs?
See all the overlay/persistence threads on fedora-livecd-list. I have
some very alpha code here-
http://filteredperception.org/downloads/overlay/
https://www.redhat.com/archives/fedora-livecd-list/2007-July/msg00158.html
In general what you are saying makes sense. I also know that Jon
Nettleton has been discussing very similar things on a thread in
fedora-devel called "a fused based initfs".
In general what you are saying sounds good to me. There definitely
seems to be some room for convergence of all these aspects of cow usage.
-dmc
Keith Adamson
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