[Borgbackup] VM backup issues

[Ken Bass]

On 11/16/2017 10:20 PM, Ken Bass wrote:
> On 11/16/2017 08:30 PM, Thomas Waldmann wrote:
>>>> You are using mtime of a regular (disk image) file or the LVM device
>>>> file?
>>> Both depending on what the underlying file is... os.stat following
>>> symlinks will indicate that the mtime of either. That appears to be 
>>> what
>>> I want.
>> Hmm, is there a strict relationship between the mtime/ctime of the
>> device file and the device contents?
> Sorry I am not sure of your question here. I know in my use case if a 
> VM has never been powered on since the last backup, the mtime/ctime of 
> the underlying LVM will not have been touched, so there is no need to 
> chunk a 30G or 100G file just for the dedup to ignore it. In my case 
> it is a waste of time / power. 

Working on this some more, now I understand your question. There may not 
be relationship between the mtime/ctime of the block device file and the 
block device contents. I think the mtime/ctime gets set to when the host 
server created the LVM block device or when a snapshot against the LVM 
was last taken. So the timestamp might represent when the host server 
was last rebooted - not related to an update of the device contents. I 
might need to use the libvirt 'hooks' to maintain a separate timestamp 
file of when the VM was last powered on.