Re: Remote Storage Mirroring vs Dataguard - Important

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 Hi Sanjay,

I actually checked few Oracle Doc and even had worked lots with Dataguard but never worked with Storage replication. All Oracle Docs as usual gave all preference and best practices to use dataguard and so thought to check with actual User experience.

I don't have much experience with Oracle but lots of mysql experience. We did have to deal with same problem so hopefully meet your criteria for commenting. Our options were to either use drdb - storage replication, mysql async or mysql sync replication (galera).

I would prefer async logical replication as others have said‎. This is because on wan, even at the best cases, you will have  some unacceptable latency. Anything over 100ms will slow down physical and sync replication as the active site wait for backup site to catch up. If its brief, all is good. But if it take long, you have decide if you need to take replication down till network issue is rectified. This may happen more than you think. 

The other problem is specific to storage replication, if the active site go done, there is a good chance it will leave the back up site in inconsistent shape too. This may be due to the network connection breaking in the middle of transactions. It could also because your storage replication copied over corruption from your active site. Dataguard would notice this corruption and replication would fail saving your backup site. Storage replication would end up taking down both sites. 

Then it's the skill. Unless you are both storage and database resource, you need to build lots of trust that your storage guy is relaying the proper information or honest when there is a mess.

My favorite reason - predictability. With logical replication, when failure show up, steps for clearing things up are petty consistent. With storage replication, the permutations of failure is far wider and fixing will vary depending on your failure. A pain when you get a nagios call at middle of the night and your brains are groggy

Regards,

William 

On Saturday, May 2, 2015 2:23 AM, Hans Forbrich <fuzzy.graybeard_at_gmail.com> wrote:

Have you looked at Oracle's documentation?

http://www.oracle.com/technetwork/database/availability/dataguardvsstoragemirroring-2082185.pdf
http://www.oracle.com/au/products/database/dataguardremotemirroring-086151.html
http://tkyte.blogspot.ca/2006/02/so-what-was-answer-part-iv.html

That last reads like a sales pitch for mirroring, but it contains some useful facts.

/Hans

On 01/05/2015 9:19 PM, Sanjay Mishra (Redacted sender smishra_97_at_yahoo.com for DMARC) 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

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