Re: External backup/restore - an idea - comments please


Hi,

hmm. Almost.

There's a caveat:
Transactions that are open at backup/archive time
can mean that at restore they need to be rolled back.
(That happens if they cannot be rolled forward until
commit - for whatever reason.)
That in turn means that ON-Bar will need to restore
those logs if you backed up and restore with ON-Bar.
Therefore it is possible, that you need to restore
logical logs that became full and were backed up
well before the actual dbspaces were backed up
with ON-Bar.

All this is not necessary for ON-Bar whole system
backup and restore (use the "-w" command line
parameter). ON-Bar whole system backup includes
the (possibly) necessary log records for roll back,
so that it can be restored without log restore, i.e.
also without need to restore earlier logs.
However, whole system backup/restore with ON-Bar
is not parallel and therefore time consuming.

One possible solution:
For the external backup and restore you do not
really need logical log backup and restore.
This is because open transaction log records are
all still contained on disk (think of long transaction
abort scenarios because of this rule). Therefore
when you externally backup all chunks, this will
conatin those logs on disk. With that the external
restore will also restore those logs and if rollback
of open transaction is necessary, it can be done
without (extra) log restore.

With version 10.00 you can do the external restore
using the appropriate ontape command for
physical external restore ("ontape -p -e"). After that
you can do a "logical restore" ("ontape -l"), but
you do not really provide a proper tape. Instead
you say you have no more tapes and it will then
bring the server to online mode (if necessary using
the logs on disk already restored externally).

That way you can backup all logs using ON-Bar.
And you don't need logs for external restore.

You can read more about that in a developerWorks
article that I wrote some time ago:

http://www.ibm.com/developerworks/db2/library/techarticle/dm-0503fuerderer/
Or look at this article (shorter and not by me):
http://www.ibm.com/support/docview.wss?uid=swg21203380

Regards,
Martin
--
Martin Fuerderer
IBM Informix Development Munich, Germany
Information Management

owner-informix-list@xxxxxxxx wrote on 05.10.2005 14:40:15:
> Hello everyone.
> Last week we've had sort of trouble - one chunk went offline after two
> mirrored disk crashed simultaneously (which was admitedly our fault).
> No problem, we take backups every night and continously backup logical
logs
> so everything was in place for warm restore (it was non-critical dbspace

> residing on that chunk).
> But, we've had problems with backup server and it's tape library.
> Fortunately, all went well and restore was successful.
>
> Of course, that posed a question: what if backup server was unavailable?
> I read through Backup and Restore Giude and started playing with
external
> backup/restore.
> At the moment we're using onbar for backup/restore with Legato Networker
as
> storage manager.
> Informix (version 10.00FC3) uses exclusively raw devices.
>
> My idea was to be able to restore (to some extent at least) an instance
even
> if the storage manager was unavailable.
> The procedure described in guide is clear to me, I just want your
opinion on
> my conclusions, which are as follows...
>
> 0. Everything that's supposed to be backed up needs to be dumped in
> filesystem and copied to remote host (which is nowhere near current
backup
> solution).
> 1. After blocking the instance I have to dump all chunks for all
dbspaces to
> filesystem, and also the previous and current logical log(s) and then
move
> it to remote host.
> 2. Since onbar can't be used to back up logical logs to filesystem (or
at
> least I wasn't able to find the way to do it) I have to use ontape
(which
> can do it in v10).
> 3. After ontape -a finishes, it marks all logical log(s), up to the
current
> one, as backed up. That means onbar will not back them up later!
> 4. The previous step isn't that bad since after external backup (and
> unblocking the instance) I'll take regular scheduled backup with onbar
> (level 0, 1 or 2, depending on the day of the week) and only logs that
gets
> backed up after that backup are needed in case of regular restore.
> 5. All of this I plan to do automatically through the script called from

> cron, during the period of lowest activity.
>
> So, before I start thorough testing my question is: how does this all
sound?
> Is this a valid way to do something like this or am I missing something
> important?
>
> Thanks everyone.
sending to informix-list
.

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