IDS Forum

AW: HDR vs. SRDF

Posted By: Andreas.KUTSCHE@spar.at
Date: Thursday, 4 January 2007, at 3:04 a.m.

In Response To: Re: HDR vs. SRDF (H.G)

Hi,

I can't see the problem with transaction rollback.
If you start your DB copy without logical restore all open transactions get rolled back anyway.
And if you start your DB copy with logical restore you will reach the same state as your source DB has (if you have all logical logs).

But there is another point: What is the main purpose of your replicated database instance?
For building testing environments or checking the production database SRDF (or similar technics, e.g. disk mirror split) are a great thing. And you don't have any impact on your production system (except a small performance loss for the time you take the snapshot). With HDR I remember a lot of threads talking about indexes, consistency and blocking, right?

But if you want a failover solution, SRDF might not be the best technic. If you do only a few snapshots a day you have the problem of rolling forward to production state (may take a long time / you may have problems to access and apply the logs).
When doing the SRDF snapshot your database copy is not consistent - if something happens at that time you might not be able to start the copied database. If you do 'continous' SRDF (always mirror on disk level) the risk of getting an inconsistent copy might even be worse - unless you use some kind of 'sync copy' which usually costs a lot of performance.
Second a continous SRDF doesn't help you against logical corruptions (user error or writes of bad blocks).

What do we do? We use SRDF (BCV mirror split as HP calls it) for (Level-0) backup and for building test environments (system copy).
We have a almost synced mirror (Continous Access as HP calls it) for failover - that mirroring doesn't use synced writes, but preserves the order of writes and theoretically that should give a consistent copy.

We have used HDR for copying/moving database instances, too. But we had sometimes errors with the HDR itself. And I worry that HDR might have impacts on large high performance databases. And if you do some data reorganization (without logging) you have to rebuild your HDR environment.

Discussions are welcome.

Regards,
Andreas Kutsche

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-----Ursprüngliche Nachricht-----

> Von: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org]Im Auftrag von
> H.G
> Gesendet: Donnerstag, 04. Jänner 2007 00:19
> An: ids@iiug.org
> Betreff: Re: HDR vs. SRDF [8093]
>
>
>
> We also do SANP exactly as Bruce mentioned but personally I
> am not very
> convenciencd. Think of a situation where a transaction was in
> progress doing
> insert etc. when we blocked server and did a SNAP. Now for
> some reason that
> transaction has been rolled back. Now DB restored from SNAP
> copy, will have
> those records but in fact prod may not be having those
> records. You can see a
> thread on this in IIUG.
>
> Cheers.
>
> ----- Original Message ----
> From: Bruce Simms <BSimms@talx.com>
> To: ids@iiug.org
> Sent: Thursday, January 4, 2007 8:47:36 AM
> Subject: RE: HDR vs. SRDF [8089]
>
> We currently use the SRDF to take a snapshot of the database
> 3 times a
> day during the online day. In the SRDF script we start the
> copies once
> they complete we issue a "onmode -c block" then break the mirror and
> issue a "onmode -c unblock" the whole process of the break leaves the
> instance locked for around 3 seconds. We then are able to use
> this copy
> for testing or backups as needed. This has worked fine for 6+ years.
> There is an EMC doc on this named ?Integrating EMC TimeFinder
> and SRDF
> Software with Informix Dynamic Server"
>
> *** Please note the new address and phone number below.
>
> Bruce Simms
> Data Base Services
> TALX Corporation
> 2330 Ball
> St. Louis, MO 63146
>
> Phone (314) 214-7703
> FAX (314) 983-3238
> bsimms@talx.com
>
> -----Original Message-----
> From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of
> GARY PRICE
> Sent: Wednesday, January 03, 2007 3:28 PM
> To: ids@iiug.org
> Subject: HDR vs. SRDF [8084]
>
> I'm setting up a high availability/DR environment for a 9.40
> database on
> AIX.
> The service provider wants me to use EMC's SRDF to
> replicate/clone data
> at the
> disk level vs. using HDR. Has anyone successfully used such a
> technology
> for
> this purpose? I prefer to use Informix native components for
> this, but
> may
> have not choice.
>
> Thanks in advance.
>
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Messages In This Thread

• HDR vs. SRDF
  GARY PRICE -- Wednesday, 3 January 2007, at 4:27 p.m.
  • RE: HDR vs. SRDF
    Bruce Simms -- Wednesday, 3 January 2007, at 4:47 p.m.
    • RE: HDR vs. SRDF
      Obnoxio The Clown -- Wednesday, 3 January 2007, at 5:42 p.m.
    • Re: HDR vs. SRDF
      H.G -- Wednesday, 3 January 2007, at 6:19 p.m.
      • AW: HDR vs. SRDF
        Andreas.KUTSCHE@spar.at -- Thursday, 4 January 2007, at 3:04 a.m.
    • Re: RE: HDR vs. SRDF
      GARY PRICE -- Thursday, 4 January 2007, at 11:32 a.m.

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