[Discuss] Backing up LVM partitions using snapshots

[markw at mohawksoft.com (markw at mohawksoft.com)]

> 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.

Why would that happen? That's what I don't understand. If you have a
mission critical failure of this sort, then you fall back to a previous
backup as your beginning and do a full backup at this point. You don't
ignore the failure and proceed business as usual.

Under normal circumstances, everything is fine. If there is a failure,
then you correct the failure. Since this is a "backed up" system, then
your main volumes have not been compromised. Like all data integrity
systems, there needs to be a process by which data is protected.

As I said a few emails back, sure, anyone can create a scenario in which
any system will fail. Losing data is a failure and there should be
workable procedures for correcting either by data forensics or
re-acquisition.