[Discuss] Backing up LVM partitions using snapshots

[Jerry Feldman]

On 12/13/2011 11:11 PM, markw at mohawksoft.com wrote:
>> On 12/12/2011 10:39 PM, markw at mohawksoft.com wrote:
>>> 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.
>> Follow closely:
>>
>> * Create file #1
>> * Do full dump.  Contains file #1 data and directory metadata.
>> * Create file #2.
>> * Do incremental dump #1.  Contains file #1 directory metadata, file #2
>> data and directory metadata.
>> * Create file #3.
>> * Make incremental dump #2.  Contains file #1 and #2 directory metadata,
>> file #3 data and metadata.
>> * Disaster strikes!  The server explodes in a ball of flame, or gets
>> eaten by Gojira or something.  You replace the hardware and prepare for
>> recovery.
> OK.
>> * Restore full dump to new server.  You now have file #1 complete.
>> * Attempt to restore incremental dump #1 and find that it is unusable.
> Using a block level store, an incremental backup is no different than a
> full backup. It appears that you are thinking of using tape or something.
> tape is dead. The backup medium is a combination of RAID and/or cloud.
>
> With block level differential backup, you can effectively replicate a
> volume with a minute amount of data.
>
> There are many levels of disaster, if just the data volume is lost, then
> it can be restored in full from any of the successful backups. if it is a
> site level disaster, then you get your backup data from offsite or cloud.
>
> I worked at a tape backup company years ago working with the QIC and DAT
> formats. OMG what a disaster. Disk sectors are cheaper and more reliable.
I've also had my issues with tape. (1) back on mainframe systems in the
early 70s, I had the tape drive burn a hole in a tape. (2) At home years
ago, I needed to restore my file system, and the tape system was simply
dead. I think I might have had write-only tapes :-). At that time, I
also had a Jaz drive with a recent backup.

A few weeks ago, I got email from the IT guy in New York looking for
$1000 worth of tapes he ordered. For some reason they were sent to me. I
work in a Regus Office (eg. HQ company)., I never saw the tapes but they
were signed for by the center manager. 6 weeks later I got a call from
the receptionist that one of the clients had a box addressed to me. It
was the tapes.

The bottom line is that there is no backup medium that is safe.. All
media degrade over time. A local RAID is good, but one lightning strike
of other glitch can render the drives dead. A cloud is probably the best
solution since it is actively managed, but you have to trust the cloud
provider, (1) to maintain the integrity of your data, and (2) the
security of your data.

-- 
Jerry Feldman <gaf at blu.org>
Boston Linux and Unix
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