[linux-lvm] Re: Unable to get XFS, ext3, reiserfs & LVM to coexist happily

[Patrick Caulfield]

On Fri, Jan 11, 2002 at 01:21:26AM +1000, Adrian Head wrote:
> In the process of trying to fix this issue I have been playing around with a 
> patch from the great SGI XFS developers.  It certainly fixes the problems I 
> was having but I'm now trying to help clean the patch up.
> 
> The problem now is that when I try to mount a ext3 snapshot using:
> mount /dev/HDA/SNAP /mnt/snapshot
> The kernel mounts the snapshot as ext2.  Is was not happening before the 
> patch and I was wondering if anyone thinks this is a problem.  As ext3 is 
> backward compatible with ext2 there doesn't seem to be any problems during my 
> testing with respect to standard file operations.  I can mount the snapshot 
> as ext3 if I use:
> mount -t ext3 /dev/HDA/SNAP /mnt/snapshot
> 
> The next problem is that when the ext3 snapshot (mounted as ext3) overflows 
> lvm generates an error in the logs:
> lvm -- giving up to snapshot /dev/HDA/XFS on /dev/HDA/SNAP: out of space
> lvm - lvm_map: ll_rw_blk for inactive LV /dev/HDA/SNAP
> 
> The 1st line I understand but the 2nd I don't.  I was hoping that some LVM 
> guru/developer could explain the 2nd line and what it means.

When a snapshot gets full it can no longer be valid so LVM makes it inactive and
fails any further I/O to it.

Because there's no more space for copy-on-write operations into the snapshot
there's no way the filesystem can be consistent. OK this isn't that nice but
it's arguably better than returning corrupted data.

patrick