[Devil-Linux-discuss] Support for LVM restore from snapshot

[Dominic R. <dl...@ed...>]

A very happy New Year to all DL developers and users!

LVM2 since 2.02.58 supports an option (lvconvert --merge) to merge back 
an LVM snapshot to an original source. This allows to you create a 
snapshot, then make 'dangerous' changes to the original source, and 
afterwards, if unhappy with the changes, simply restore the snapshot to 
recover the original data.

This is potentially very useful (as in, how come LVM didn't always do 
this?) and is supported by LVM 2.02.72 as found in DL 1.4 (and I think 
1.4.1 tho I am not yet using it, sorry), but I don't think it will work 
because the man page [for LVM 2.02.76] says "To check if your kernel 
supports this feature, look for 'snapshot-merge' in the output of 
'dmsetup targets'" And when I do this in DL I don't see snapshot-merge 
listed.

Info about kernel device-mapper snapshot support here: 
http://alinux.tv/Kernel-2.6.34/device-mapper/snapshot.txt
LVM2 changelog here: ftp://sources.redhat.com/pub/lvm2/WHATS_NEW

I confess I haven't tested it because my DL machine is a production 
system and I don't want to risk upsetting it. Is someone able to try it 
on a test DL system by creating an LVM snapshot (e.g. of /home), making 
changes to the original and then merging back the snapshot? If the 
kernel support is critical and is missing then I presume this will fail, 
whether safely or not I have no idea.

If the kernel support is needed, can I ask for this option 
(snapshot-merge) to be added to DL kernel for the next mini-release, 
please (and upgrade LVM to 2.02.79)? I can put this request on Mantis if 
preferred...

Dominic