In a large system with lots of components you can't even guarantee that
local storage will accurately contain the blocks that Oracle wrote.
Electrical glitches, cosmic rays - don't laugh, you can look up the IBM
paper detailing the probability of you like - failing controllers and all
sorts of other unexpected events.
The work on T10 Data Integrity Format/ Data Integrity eXtensions
demonstrates this, for a local system but is not yet widely supported.
Maybe when it becomes available for synchronous remote SAN replication you
can start to be comfortable that your DR site will actually recovery your
database. Until then your DR is only as good as your last trial recovery.
Else use Data Guard, which will let you know when you have a corrupt block.
Regards
JT
On Wed, 6 May 2015 16:24 MARK BRINSMEAD <mark.brinsmead@xxxxxxxxx> wrote:
Yes. Generally, this can be a *big* plus. The licenses needed to operate
a standby database can cost hundreds of thousands of dollars. This is
probably the only reason I would consider storage-level replication for
DR. (It can be used for all sorts of other clever purposes elsewhere,
though.)
Of course, the need to restore/install Oracle software, and maybe
configure some devices (e.g., if using ASM) could make your failover a
little-less-than-instantaneous.
Personally, I have higher confidence in a dataguard standby -- if for no
other reason that I know it is ready for failover at a moment's notice, and
I can validate the integrity of the database as often as if I choose to.
But sometimes there are compelling reasons to sacrifice a little confidence.
On Wed, May 6, 2015 at 10:50 AM, Mladen Gogala <
dmarc-noreply@xxxxxxxxxxxxx> wrote:
On the other hand, you can do storage replication, without consuming an
Oracle license. Essentially, you can just replicate your storage and, if
switchover is needed, restore the Oracle software from backup, bring up the
instance and go on. Saving on Oracle licenses is a BIG plus.
On 05/05/2015 02:22 AM, Svetoslav Gyurov wrote:
Hi Sanjay,
I used storage replication many times to copy prod to dev or take a
snapshot before some major activity but never used it in a way as a DR.
To answer your questions:
- I would prefer DG because it's much more flexiable. You've got an idea
what is the transport lag, apply lag and what is the state of your standby.
You can open the standby as readonly, ADG or ever snapshoot standby to do
some testing. Switchover is just a matter of one command through the
broker. I cannot see neither of these happening with the storage
replication.
- It should be fine, as long as you replicate all the ASM LUNs. If you
open the standby database you'll always have to do instance recovery, keep
that in mind.
- Yes, you can have your storage replication in SYNC. Pretty much it's
similar to DG - the blocks from the first storage arre written to the cache
of the second storage and they an acknoledgement is sent.
- Not sure what the question is but if you have a GAP the storage
systems are smart enough - and because we are only replicating blocks they
can assisiliy recover the gap and become in sync again.
- The fastest and safe way to bring the standby database in consistent
state is by using DataGuard broker.
- Modern storages have the option to change the direction of the
replication so this shouldn't be a problem.
Regards,
Sve
On Sat, May 2, 2015 at 4:19 AM, Sanjay Mishra <
dmarc-noreply@xxxxxxxxxxxxx> wrote:
Can anyone share their views on the following on Real practical
experience with the setup in their environment. I had worked with dataguard
but never with Storage Replication for Disaster recover.
Some points for the required environment which can affect or help in
providing or sharing the experience
- Oracle 11g 2-Node RAC setup using ASM on both Primary and DR site
- Database size range from 1-5Tb
- Database has lots of DML activites on daily basis
Questions:
- What is the best option to be used for Disaster Recovery when has
to choose Storage Replication vs DataGuard for RAC setup and if can
provide
why you think one preferred over other as per your experience ?
- Does there can be issue if Primary storage or server crashed and
Recovery either failed to start the Datbase on DR or lost some data ?
Keeping in mind that we are working in SYnc Mode.
- Is Storage mirroring can be setup so that both Primary and Remote
storage is almost SYNC like Synchronous Data Giuard Setting ?
- Is it possible that we may loose the DR location and Storage
Replicated environment failed to start ?
- Which one is faster to bring Database live, Storage mirrored DR
env or Dataguard based environment?
- How to go back or switch back to original Primary when you have
done switchover initially to DR location ? In Oracle Dataguard we can go
back using Flashback DB feature and reinstantiate the database
- Any other Pros and Cons for both option as well as any good Link
to be checked.
TIA
Sanjay
--
Mladen Gogala
Oracle DBAhttp://mgogala.freehostia.com
