[CentOS] Rsync and differential Backups

Sat Nov 14 17:01:23 UTC 2015
Mark Milhollan <mlm at pixelgate.net>

On Fri, 13 Nov 2015, Gordon Messmer wrote:

>Breaking a RAID volume doesn't make filesystems consistent, 

While using LVM arranges for some filesystems to be consistent (it is 
not always possible), it does nothing to ensure application consistency 
which can be just as important.  Linux doesn't have a widely deployed 
analog to Windows' VSS, which provides both though only for those that 
cooperate.  On Linux you must arrange to quiesce applications yourself, 
which is seldom possible.

>Breaking the
>RAID will duplicate UUIDs of filesystems and the name of volume groups.  

Making an LVM snapshot duplicates UUIDs (and LABELs) too, the whole LV 
is the same in the snapshot as it was in the source.  There are ways to 
cope with that for XFS (I usually use mount -ro nouuid) -- ext2/3/4 
doesn't care (so just mount -r for them).  If the original filesystem 
isn't yet mounted then a mount by uuid (or label) would not be pretty 
for either.  And that's just two filesystems, others are supported and 
they too will potentially have issues.