On 11/24/05, Maciej Żenczykowski maze@cela.pl wrote:
Do any Linux filesystems (besides XFS) support freezing? (ie. in conjuction with LVM snapshots this can allow a mounted filesystem to be frozen [freezing all processes writing to this filesystem] in a valid state (with possibly dangling unlinked files), the device can be snapshotted via LVM, and the original filesystem unfrozen - the snapshot now contains a valid snapshot in time of the original filesystem - with no corruption.
I'm reasonably certain that LVM+ext3 automatically makes consistent snapshots (no freezing necessary). See http://www.tldp.org/HOWTO/LVM-HOWTO/snapshotintro.html for (slightly) more details.
Can a snapshotted LVM (the snapshot, not the original filesystem) be modified (I assume snapshots are purely readonly...) - so as to remove the dangling deleted/unlinked files and possibly modify the uuid (I realize there is a nouuid mount option for XFS).
Under LVM2, snapshots are read-write; however, LVM2 isn't currently reliable on CentOS 4 or the upstream release. (See the thread starting at http://marc.theaimsgroup.com/?l=centos&m=113155162316509 for details.)
And the last question: is there some sort of filesystem which supports generating 'in-filesystem' snapshots
It looks like there's a research project underway at http://www.ext3cow.com/, and there's the Wayback filesystem for FUSE at http://wayback.sourceforge.net/, but I've no idea how usable either is.