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I've modified a script to backup live xen images with dar. This script uses lvm to snapshot a running VM disk, then mount it read only and uses dar to create an incremental backup. The script is a derivative of a script I've found on the net [1]. There is still a small problem with journaled file system that even if the fs is frozen before taking the snapshot, for some reason, even if I mount it read only, the kernel module tries to go through the journal to recover the fs. I'm worried that this might lead to data corruptions...

Not a tutorial, just few lines to write down what I've done.

This command gives you information about all virtual groups

Then, to create a logical group :

the  -l option specifies the number of extent to allocate for this lv . You can see the number of available extents for a vg with the command above. This is useful to know when you want to create a lv using all the available space.

Then let's create an xfs fs on this lv :