[CentOS] CentOS Server Backup Options: at runlevel 5? ... w/snapshot

Markus Falb markus.falb at fasel.at
Fri Mar 16 15:44:50 EDT 2012


On 16.3.2012 19:53, Les Mikesell wrote:
> On Fri, Mar 16, 2012 at 1:19 PM, ken <gebser-Qz+AbkVSZgBWk0Htik3J/w at public.gmane.org> wrote:
>>
>>>>
>>> I find that LVM snapshots are useful to insure data integrity.  for
>>> example, I backup my mysql databases by stopping the mysql server,
>>> taking an LVM snapshot and restarting it.  The whole snapshot process
>>> probably takes less then 15 seconds.  Then I backup the snapshot LVM and
>>> it doesn't matter how long it takes.  You must make sure that your
>>> snapshot volume is large enough that you won't run out of space before
>>> deleting the snapshot.
>>
>> Thanks for the tip.  The details of how a snapshot works has long evaded
>> me.  For example, when files are open but unsaved, what is written to
>> the snapshot...?  And is the entire contents of a file recorded by the
>> snapshot... or something else?
> 
> LVM snapshots just present a view of the disk as it was when the
> snapshot was taken.  To do that, whenever you write to the disk with a
> snapshot active, it first copies the old data into the snapshot.

Note that this results in degraded write performance while the snapshot
is active. Basically you have to "double write", at least.

-- 
Kind Regards, Markus Falb

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