ADSM-L

Re: [ADSM-L] Nervous Nellies and TDPO -- feasible?

2007-11-21 11:43:59
Subject: Re: [ADSM-L] Nervous Nellies and TDPO -- feasible?
From: David McClelland <David.McClelland AT REUTERS DOT COM>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Wed, 21 Nov 2007 16:41:31 +0000
Pierre, great answers.

I'd add that, depending upon your business recovery requirements, you
may wish to embrace disk/array/snapshot based backup and recovery tools
_as well_ as RMAN. If you've, for example, a 5TB database and a
business-stated 4 hour recovery time objective for your service/database
then you're going to have to drive disk/tape very hard indeed to meet
your service recovery requirements with RMAN alone. 

For larger databases with tight recovery times, RMAN > TSM can be used
as a complement to disk/nearline based recovery methods (e.g. BCV, Clone
or Snap on EMC storage hardware), providing for longer-term retention
(e.g. for regulatory requirements) and more granular recoveries (e.g.
table level rather than the whole database). If the majority of recovery
scenarios to get a service back online are within 24 hours from the
point of backup, a daily BCV/Snap whatever might meet this very ably,
regardless of whether you're also backing up to offline media via RMAN
or BA client backups.

In terms of responding to a recovery point requirement (e.g. the
business can afford to lose no more than x days/hours/minutes' worth of
data in a disaster), RMAN can make sure your archived redo logs are
shipped out very efficiently, and what's more make a pretty easy job of
recovering them too. Another thing to consider is an RMAN Recovery
Catalog - I'll not go into detail here, but do look this up if you
aren't already familiar with the concept.

In a nutshell, as well as looking at the backup technology, take pains
to look at what your _recovery_ requirements are - regardless of how
much more efficient RMAN may or may not be than BA client backups, if
either alone won't help you to meet your service RPO/RTO SLAs then you
may in addition need to look elsewhere, for example disk array/nearline
backups.

HTH,

David McClelland
London, UK

-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
CAYE PIERRE
Sent: 21 November 2007 15:56
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: [ADSM-L] Nervous Nellies and TDPO -- feasible?

>       1) RMAN doesn't deal with non-transactional DB data loads well.
>          (i.e. data loaded not through the usual INSERT/UPDATE
>          methods, but done via sqlldr. This doesn't generate redo
logs.)
> 
>          True or false?

RMAN back-up data's which are in all tables, whatever they had been
loaded or inserted.

>       2) RMAN requires a recovery database be created to do recoveries
to
>          (instead of recovering to original database/tablespaces
in-place).
> 
>          True or false? I thought RMAN didn't need an intermediate
temp
>          database and could restore directly 'in-place'.

False. Rman is able to restore databases on original place, or anywhere
you wish. It only requier a large enough database.

>       3) Will RMAN guarantee a good point-in-time view of DB data?

It depend of the regularity and disponibility of redo logs, which need
to backed-up too...

>       4) Same as #3 above, but what if the DB is currently processing
>          a large series of INSERTs or UPDATEs or sqlldr run, will RMAN
>          only send data that was present at the moment of backup
start?

Rman perform backup wwhich will be consistent; whatever happend on the
db as insert delete, update and so. RMAN is a part of oracle product,
not an external actor, and act at a logical level of data's. At the end
of the rman backup, data's are consistent and could be restored in a
consistent state.

>       5) Does RMAN/TDPO use scale to really large DB setups? Say, tens
>          or hundreds of terabytes? Or even sub-10 TB?
> 
>          Anybody using TDPO well with terabytes of Oracle data? (I
>          think they're hoping for assurances that it really does work
>          in the real world at that scale.)

I'd only experienced db of 2/3 Terabytes and it work fine, whithout any
particular configuration on Oracle side.
See Oracle guides for best practices concerning very large databases.

>       6) How does Oracle RMAN know what rows to send for an
>          incremental backup? Does Oracle maintain a bitmap of some
kind
>          or time-based logging of changed blocks or something? Any
>          pointers to whitepapers or information on how it works behind
>          the scenes?

On Oracle 10g, Oracle maintain a bitmap of changed block.
So incremental backup are faster than full backup on 10g. 
On Oracle 9i, Oracle scan all filespaces for changed block.
So incremental backups can be slower that full but, from my experience,
it is almost the same.

>       They would prefer to utilize Veritas DB Edition (DBED)
checkpoint 
> feature which is where a script runs to put all tablespaces in backup 
> mode, brings DB-based filesystems to a consistent state, generate a 
> checkpoint (snapshot-like) of the filesystem, then brings all 
> tablespaces back to online mode. The TSM BA client then mounts the 
> most recent checkpoint R/O then backs it up at the file level.
> 
>       The problem with the above approach is this essentially results
in 
> what amounts to a full backup every single time it kicks off. That's 
> just not practical in terms of tape cost as well as the length of 
> backups.
> 
>       I see TDPO as the only practical choice for much faster and more

> frequent backups (and restores) and is guaranteed for consistent 
> point-in-time views of DB data. The BA client was also not meant to 
> back up databases (though it *could* do so if properly quiescied).

Nothing more to said. You're right. TDPO act only as a library manager
for RMAN. It is RMAN which is the principal actor on back-up.
RMAN is an integrated Oracle solution to backup Oracle databases.
Integrated mean that it work fine at logical level of the data's. The
use of RMAN, for offline (full) or online (incremental) backup is a
guarantee for consistencies of backed-up data's. 
You work with Oracle 10g, so incremental back-up will be fast and you
will save storage and time.

>       My issue? I don't have enough meaty information yet to put
concerns 
> to rest, and I'd really like to make use of TDPO after paying out 
> $16,000. Any info would be much welcome.

Search on IBM/redbooks. There are redbooks about RMAN and TDPO (sorry I
don't remind reference number...).

Pierre


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