Re: Replicated File System Consistency

From: hpuxrac <>
Date: Fri, 2 Jan 2009 17:01:00 -0800 (PST)
Message-ID: <>

On Dec 29 2008, 11:53 am, Pat <> wrote:
> So we've got a half dozen or so Oracle 10G ( servers with
> production data on them.
> Historically, we ran them with direct attached RAID arrays, but
> recently we moved them to a new data center with a netapp 3040 SAN.
> Performance on the new hardware seems about the same; SAN is
> theoretically faster but I think there's more latency so from what I
> can see its a wash.
> Question I have though is about dr and consistency.
> We have a second san offsite.
> I can configure san mirroring to mirror our primary san off to another
> data center (more accurately I can ask the san guys to do so).
> In the event of a catastrophy at my primary center, can I mount the
> mirror copy of the database in dr, go through a recovery, and be
> relatively comfortable I've got a conistent data set?
> I know that if I pull the plug on the machine, Oracle commits that,
> post recovery, I won't lose any commits and it'll be consistent
> (although the recovery may take a while).

Dunno what you mean here "Oracle commits that post recovery" ... it don't sound right.

If you mean that when instance recovery is performed oracle backs out any uncommitted transactions ... fine.

> Does the same commitment hold if I'm using a lower level (block level)
> replication technology and the replication fails in some unexpected
> place?


First you have to differentiate between storage based synchronous and asynchronous replication. Two fundamentally different answers and different implications.

With asynch you risk losing data at the DR site and write order dependencies must be handled between and across LUNS. With EMC Clariion technology you use consistency groups ... dunnot what Netapp equiv is or if they support async.

Synchronous replication requires bandwidth and impacts latency of writes at the primary site. Async has no impact on writes at primary site.

> Sorry if this is an obscure question, but I don't understand the
> interaction of Oracle's file system with the SAN well enough to make
> intelligent recommendations to the DR guys.

I am sure there are Netapp manuals you can look at. Received on Fri Jan 02 2009 - 19:01:00 CST

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