Re: ZFS filesystem - supported ? - Mailing list pgsql-general

On 10/25/2021 10:13 AM, Stephen Frost wrote:
> Greetings,
>
> * Mladen Gogala (gogala.mladen@gmail.com) wrote:
>> On 10/23/21 23:12, Lucas wrote:
>>> This has proven to work very well for me. I had to restore a few backups
>>> already and it always worked. The bad part is that I need to stop the
>>> database before performing the Snapshot, for data integrity, so that means
>>> that I have a hot-standby server only for these snapshots.
>>> Lucas
>> Actually, you don't need to stop the database. You need to execute
>> pg_start_backup() before taking a snapshot and then pg_stop_backup() when
>> the snapshot is done. You will need to recover the database when you finish
>> the restore but you will not lose any data. I know that pg_begin_backup()
>> and pg_stop_backup() are deprecated but since PostgreSQL doesn't have any
>> API for storage or file system snapshots, that's the only thing that can
>> help you use storage snapshots as backups. To my knowledge,the only database
>> that does have API for storage snapshots is DB2. The API is called "Advanced
>> Copy Services" or ACS. It's documented here:
>>
>> https://www.ibm.com/docs/en/db2/11.1?topic=recovery-db2-advanced-copy-services-acs
>>
>> For Postgres, the old begin/stop backup functions should be sufficient.
> No, it's not- you must also be sure to archive any WAL that's generated
> between the pg_start_backup and pg_stop_backup and then to be sure and
> add into the snapshot the appropriate signal files or recovery.conf,
> depending on PG version, to indicate that you're restoring from a backup
> and make sure that the WAL is made available via restore_command.
>
> Just doing stat/stop backup is *not* enough and you run the risk of
> having an invalid backup or corruption when you restore.
>
> If the entire system is on a single volume then you could possibly just
> take a snapshot of it (without any start/stop backup stuff) but it's
> very risky to do that and then try to do PITR with it because we don't
> know where consistency is reached in such a case (we *must* play all the
> way through to the end of the WAL which existed at the time of the
> snapshot in order to reach consistency).
>
> In the end though, really, it's much, much, much better to use a proper
> backup and archiving tool that's written specifically for PG than to try
> and roll your own, using snapshots or not.
>
> Thanks,
>
> Stephen
what about BTRFS since it's the successor of ZFS?

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