SNAP & SAN
Hi All, HP-UX B.11.11.11 IDS 9.40.FC4 We have got SAN setup which has got all chunks (raw devices) etc. etc. A process runs from cron which takes a snapshot (SAN view point). Before snap, IDS is blocked and unblocked after snap. What worries me, if some process is running within transaction and hasn't been completed when server had been blocked. Regardless of transaction committed or rolled back, will snap restore a true image of database at that point in time, if need arises. Can some one please share their experience in this scenario ? TIA
Apologies. I would have mentioned in earlier post that we do have onbar
for Level 0 & logical log backup but wanted to know about SANP in
particular.
TIA
<hariog@yahoo.com> wrote in message news:1155087171.426708.317840@i42g2000cwa.googlegroups.com... > Hi All, > > HP-UX B.11.11.11 > IDS 9.40.FC4 > > We have got SAN setup which has got all chunks (raw devices) etc. etc. > A process runs from cron which takes a snapshot (SAN view point). > Before snap, IDS is blocked and unblocked after snap. > > What worries me, if some process is running within transaction and > hasn't been completed when server had been blocked. Regardless of > transaction committed or rolled back, will snap restore a true image of > database at that point in time, if need arises. Actually what you will end up with after external restore is a true image of the database server's state at the time of the last checkpoint.
Hi,
I try to clarify this a bit more ...
After restoring the snapshot, you have an "image" of the data
exactly as it was while the server was blocked when taking
the snapshot. The command "onmode -c block" explicitly
writes a checkpoint so that all data will be on disk and the
disks will be physically consistent. Only after that will the
command "onmode -c block" return the prompt to the user.
However, this physical consistency does not mean that things
are logically consistent, i.e. regarding transactions, etc.
Because of this restoring the snapshot actually corresponds
to a physical only restore of the dbspaces.
After a physical only restore, a logical restore should follow
to make things logically consistent. This is the logical restore phase.
The minimum work required to be done in general is to roll back
any open transactions. This needs to be done even if there are
no logs to restore. If there are logs to restore, log records in them
can be rolled forward starting at the point of the block checkpoint
going forward.
While restoring the snapshot with external means corresponds to
the physical restore phase, ON-Bar or ontape is used to
accomplish the logical restore phase.
I hope this makes things somewhat clearer.
BTW: you may want to consider also saving some files in directory
$INFORMIXDIR/etc/ at the same time when you are doing the
snapshot (i.e. as part of the snapshot, e.g. .../etc/oncfg* file).
Regards,
Martin
--
Martin Fuerderer
IBM Informix Development Munich, Germany
Information Management
IBM Information On Demand Global Conference
October 15-20, 2006, Anaheim, California
see http://www.ibm.com/events/informationondemand
informix-list-bounces@iiug.org wrote on 09.08.2006 09:23:23:
> <hariog@yahoo.com> wrote in message
> news:1155087171.426708.317840@i42g2000cwa.googlegroups.com...
> > Hi All,
> >
> > HP-UX B.11.11.11
> > IDS 9.40.FC4
> >
> > We have got SAN setup which has got all chunks (raw devices) etc. etc.
> > A process runs from cron which takes a snapshot (SAN view point).
> > Before snap, IDS is blocked and unblocked after snap.
> >
> > What worries me, if some process is running within transaction and
> > hasn't been completed when server had been blocked. Regardless of
> > transaction committed or rolled back, will snap restore a true image
of
> > database at that point in time, if need arises.
>
> Actually what you will end up with after external restore is a true
image of
> the database server's state at the time of the last checkpoint.
>
>
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