[CentOS] [Marketing Mail] Re: LVM and Backups

Wed Sep 19 08:54:18 UTC 2018
Alessandro Baggi <alessandro.baggi at gmail.com>

Il 19/09/2018 09:28, Lange, Markus ha scritto:
> On Wed, 2018-09-19 at 08:55 +0200, Alessandro Baggi wrote:
>> Il 18/09/2018 17:14, Gordon Messmer ha scritto:
>>> On 9/17/18 11:38 PM, Alessandro Baggi wrote:
>>>> Il 17/09/2018 22:12, Gordon Messmer ha scritto:
>>>>> That doesn't look right.  It should look more like 1) stop or
>>>>> freeze
>>>>> all of the services (httpd and database), 2) make the snapshot,
>>>>> 3)
>>>>> start or thaw all of the services, 4) mount the snapshot, 5)
>>>>> back up
>>>>> the data, 6) remove the snapshot.
>>>>
>>>> About database setup I perform backups via pg_dump so how the
>>>> snapshot
>>>> affects pgsql database? What your suggestion I must perform
>>>> database
>>>> backup copying only filesystem file and not pgsql.sql database
>>>> dump?
>>>
>>>
>>> If you want a plain-text dump of the DB, you can do that before the
>>> LVM
>>> snapshot sequence: 1) pg_dump, 2) stop or freeze all of the
>>> services
>>> (httpd and database), 3) make the snapshot, 4) start or thaw all of
>>> the
>>> services, 5) mount the snapshot, 6) back up the data, 7) remove
>>> the
>>> snapshot.
>>>
>>> Typically, the reason you want to use snapshots for the backup is
>>> that
>>> you don't need to do pg_dump to get a consistent DB backup,
>>> though.
>>> pg_dump style backups are extremely slow to restore.  If you freeze
>>> the
>>> DB, make a snapshot, and thaw, you can make a safe, consistent
>>> backup of
>>> the DB files directly, and restore in minimal time.
>>>
>>>
>>>>> Are you using bacula's built-in snapshot support, or are you
>>>>> rolling
>>>>> your own?
>>>>
>>>> No I'm using pre/post job script where I have lvm commands to
>>>> create
>>>> and destroy snapshot volume.
>>>>
>>>
>>> I really recommend using a ready-made process rather than rolling
>>> your
>>> own.  Bacula has snapshot support.  Alternately, my project can
>>> manage
>>> snapshots and handle freezing / thawing PostgreSQL services.  I
>>> think
>>> it's a better option than Bacula's, but either is better than
>>> reinventing this wheel.
>>>
>>> https://bitbucket.org/gordonmessmer/dragonsdawn-snapshot
>>>
>>> _______________________________________________
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>>> https://lists.centos.org/mailman/listinfo/centos
>>
>> Thank you for the suggestion.
>>
>> I don't know why I considered pg_dump better then filesystem backup.
>> At
>> this moment I prefer pg_dump because in this mode I can restore data
>> on
>> different version of postgresql. With filesystem dump I can restore
>> only
>> for a specific version. Is right?
>>
>> I will give a try.
>>
>> Thank you again for suggestions.
>>
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>> https://lists.centos.org/mailman/listinfo/centos
> 
> Hi,
> 
> an restore may need additional attention while restoring database files
> to a different version of postgres. However, while the versions does
> not differ that much (an official upgrade path exists, or no layout
> change was made between the versions) the files work just as if you
> updated the database using yum (check out spec file from source pkg to
> find out what happens on package upgrades, you may need to do upgrade
> steps manually).
> 
> This should only be a problem when you try to restore to a new major
> version of postgres. But in that case I would recommend an additional
> pg_dump backup to have a save fallback.
> 
> best regards
> 
> ps: I do not use postgres, please understand my testimony as not tested
> practically.
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> 

Thank you for the suggestion.

Best regards