Re: alter database suspend

From: Volker Hetzer <firstname.lastname_at_ieee.org>
Date: Wed, 18 Oct 2006 17:12:49 +0200
Message-ID: <eh5g9h$829$1@nntp.fujitsu-siemens.com>

hpuxrac schrieb:
> Volker Hetzer wrote:
> .

>>> Are you using suspend in some of your current processing?  Do you have
>>> concerns about why it was developed and how it has been placed?
>> I'm just curious.
>> We use 10g on Linux, one copy of the archivelogs on our netapp filer (nfs).
>> Last month we had a controller crash on the database (we could recover
>> complety) and since then we think of mirroring some stuff on a netapp
>> filer. We started out with the archivelogs, no snapshots, to get a feel
>> for it.
>> The question for me is, can we make use of the snapshotting capabilities
>> in some way?

>
> Still confused here. Usually snapshotting is done in a vendor
> proprietary way from within a storage device ( set of storage devices).
> For instance with EMC you can have BCV's ( snapshots ). You decide
> when to establish a snapshot, split off a snapshot, or restore from a
> snapshot. It's done on a hardware level via looking at the
> blocks/tracks that have changed. All the disk/LUNs are within the EMC
> including the snapshots

Yes, but if you "just" take a snapshot, you typically get useless data, at least for databases.
To do a backup of datafiles with a filer, you have to:

sqlplus> alter database begin backup; --puts tablespaces in backup mode
sqlplus> host rsh -l username filer.domain snap create datafile volume
sqlplus> alter database end backup;


>> I guess, performance aside, it would make sense to have a controlfile on
>> the filer, on a separate volume. In case of a crash we could then decide
>> to use the current or a previous controlfile.

>
> That's just placing a controlfile on another disk somewhere. Not
> involving mirroring or snapshots. Or are you talking about some other
> setup?

I would /like/ to snapshot the controlfile too, maybe hourly.

>> The same reasoning applies to a lesser extent to archived logs, even if
>> it is unlikely that arc messes up logs already archived.
>>
>> Since oracle's backup mode is for tablespaces I guess that suspend
>> is for the other files and I'm wondering about the granularity of
>> it.

>
> Sounds like a question to submit to oracle support.
Will do that.

>> Will suspend guarantee a completely written controlfile?
>> Ditto for archived logs?

>
> How exactly are you thinking about using suspend? I still don't quite
> understand where you are going.

sqlplus> alter database suspend;
sqlplus> host rsh -l username filer.domain snap create controlfile volume
sqlplus> alter database resume;

The whole thing is supposed to take about one second.

>

>> We have no pressing need, since rman works nicely for us.
>> But I'd still like to understand it because it always pays
>> to know ones options.

>
> I am not aware of any of the rman documentation that documents or
> recommends using suspend anywhere ( live and learn ).
Of course. Rman has no need of snapshots. But after one defective board and now a crashed controller I'd like to ensure recoverability a bit more often than just once a day.
The alternative is to run rman hourly, just for the controlfile and archivelogs. Would be fine too, but still I would like to know whether something equivalent could be done with the filer. If I would just snap half an archivelog/controlfile it would be useless.

Lots of Greetings!
Volker

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Received on Wed Oct 18 2006 - 10:12:49 CDT