[Discuss] Backing up LVM partitions using snapshots

[Richard Pieri]

On 12/12/2011 1:33 PM, Mark Woodward wrote:
> Why would they be missing? Sure, any storage system can be corrupted 
> and you would loose data. Loss of data is a risk in every system. Even 
> if you did a full backup every night, there is no guarantee you won't 
> lose data. The system I describe reduces the amount of data that must 
> be saved. This actually increases reliability. I'm not saying anything 
> new at all. A lot of vendors are doing this. 
I create a 12K file on your 8K block volume.  This marks a number of 
blocks in the block map as changed:
* Two blocks for the file data.
* One or more blocks for the inode list stored in the directory data.
* Possibly the file system superblocks.

You do your first delta dump.  I then create another file in the same 
directory.   This marks the directory block(s) as changed and will be 
dumped on the next run.

You then lose the intermediary dump containing my first file's data.  
When you skip and "overlay" the successive dumps then the directory 
blocks in question will contain an inode list, file name and metadata 
for a file that does not exist.  The file system is in an inconsistent 
state.

How do you fix this?