Hi Mark,
After reading your comment about the online redologs I realized that I omitted
an important piece of information when describing the snapshoting process. So,
I'd like to provide an additional clarification.
After "alter system archive log current" and prior to snapshoting the file
system with the archivelogs I'm querying the latest archived SCN. The database
will be recovered until this SCN in the course of rollback/clone process. This
means that the online redo logs will not be used at all when rolling back to
the "hot" snapshot. In contrast, the snapshot online of redo logs is only used
when rolling back the "cold" snapshot.
In addition, I'd like to point out that there is a boundary condition that
might render the snapshot unusable. What I mean by that is if new datafiles
were created in the short time period between data file snapshot and control
file backup, the files will be referenced in the control file backup, but not
contained in the snapshot. Therefore, it is necessary check whether new files
were created in the mentioned time period if there is a possibility that new
datafiles are created by some automatic process which might run concurrently
with snapshoting.
Hence, the process would look like this:
Alter database begin backup;
Snapshot file systems with data files
Alter database end backup;
alter database backup controlfile to trace as .. ;
raise exception if new files were created since the snapshot
alter system archive log current
save the scn for the recovery => scn = select max(next_change#) from
v$log_history
Snapshot file systems with the archivelogs
Finally, I'd like to thank you for making me aware of the mistake I did in my
previous e-mail.
Best regards,
Nenad
http://nenadnoveljic.com/blog/
From: Mark W. Farnham [mailto:mwf@xxxxxxxx]
Sent: Mittwoch, 10. Januar 2018 17:35
To: Noveljic Nenad; christopherdtaylor1994@xxxxxxxxx; 'ORACLE-L'
Subject: RE: For those using snapshots of Prod Disk Groups - Question
If you reload the snapshots containing the online redo logs you will likely be
in for an unpleasant surprise.
Online redo logs should only be on a special backup set for complete point in
time recovery (if they are backed up at all, which is a discussion of the
relative danger of reloading online redo logs when you didn’t mean to versus
someone deleting them before they are archived in rotation or backed up by some
other means.)
Backing up the current online redo logs (and the control files) to a special
media set is a valid first step of recovery that allows you multiple attempts a
complete recovery if something goes bump in the night during recovery. This all
applies to recovering physical backups unmanaged by RMAN, which has been
essentially the same since 6.0.
Find yourself a test host network isolated from your real host and practice
this snapshot recovery a few times to be certain of what you have.
The other thing is to make sure the archive log current completes before you do
the snapshot archive logs operation.
mwf
From: oracle-l-bounce@xxxxxxxxxxxxx<mailto:oracle-l-bounce@xxxxxxxxxxxxx>
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Noveljic Nenad
Sent: Wednesday, January 10, 2018 10:53 AM
To: 'christopherdtaylor1994@xxxxxxxxx'; ORACLE-L
Subject: RE: For those using snapshots of Prod Disk Groups - Question
I’m using the following process for snapshoting database in archivelog mode
without stopping it:
Alter database begin backup;
Snapshot file systems with data files and online redo logs
Alter database end backup;
alter database backup controlfile to trace as .. ;
alter system archive log current ;
Snapshot file systems with the archivelogs
In the case of rollback:
Stop the database
Rollback all file systems
Recreate controlfile and recover
(Change dbid to avoid conflicts in RMAN)
I also use snapshots for “database cloning” where a new database is created
based on the snapshot. The process is similar to rollback except that new file
systems are created based on the snapshot and the controlfile backup (as trace)
has to be edited to reflect the name of the new database and new file locations.
In case that you’re stopping the source database when doing the snapshot, the
FRA is not necessary.
I rely on ZFS instead of storage copy-on-write functionality.
Last but not least, as you correctly mentioned, snapshotting is no replacement
for backup/recovery, but is very useful when doing application and database
upgrades. It is also invaluable for quick provisioning of development databases.
Best regards,
Nenad
http://nenadnoveljic.com/blog/
From: oracle-l-bounce@xxxxxxxxxxxxx<mailto:oracle-l-bounce@xxxxxxxxxxxxx>
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Chris Taylor
Sent: Mittwoch, 10. Januar 2018 16:21
To: ORACLE-L
Subject: For those using snapshots of Prod Disk Groups - Question
For those of you utilizing storage snapshots of your Prod disk groups, do you
also include the FRA contents in your snapshots?
There's an open question we're discussing about whether we need the FRA
contents as part of the snapshot.
(We're only using snapshots as protection against screw ups - not as a
backup/recovery option. So if we really, really had to we could restart the
database from a previous snapshot - or clone the snapshot to a utility server
to do some data restoration)
I'm thinking the FRA contents don't need to be part of the snapshot but I could
be mistaken.
Chris
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