> 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. > Thanks for you comments. I looked at your code. I think it looks good, however, I was looking for a more general anaconda option. I may be wrong, but the heavy use of loopbacks seems problematic as it leads to filesystem dependencies. However, it may be needed in your case. Can't you just use another partition on a r/w media for your CoW? Do you think anaconda should get involved with loopback mounts? I'm looking for an anaconda option that is a little different from the classic ext[23] or lvm partition setups by extending ext[23] setup to include CoWs, as these seem to be fundamentally different than lvm. However, the proposed ?/etc/cowtab? could be parsed for loopback mounts, although dependency logic would have to be observed somehow. Although, my brain swells when thinking about loopback mounts of the root filestem :) Regards, Keith Adamson
