RE: RE: RE: Double Take and Oracle

Nick Wagner Tue, 15 Oct 2002 10:37:23 -0700

Title: RE: RE: RE: Double Take and Oracle

A little clarification....

---cut---
The reasons for this are wrapped around Oracle's "write as little as needed and
do so as seldomly as possible" idea.
---end cut---

is not really true.

When a tablespace is placed into hot backup mode, Oracle does not delay any writes to the datafiles. It continues to write to them like nothing changed. However, the major change (and performance hit) occurs because Oracle write more info to the redo logs. Instead of just writing the changes for that row to the redo log, it will now write the entire database block to the redo log. This is a reason why a lot of hot backup scripts, place only the tablespaces your are currently copying into hot backup mode.

-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, October 15, 2002 9:44 AM
To: Multiple recipients of list ORACLE-L
Subject: Re:RE: RE: Double Take and Oracle

Eva,

First things first, Oracle gets to be a bear when your trying to move a
database as you are while it's running. The first point to settle is that
Double Take is not doing something that is incompatible with Oracle, like making
an ASCII vs. BINARY copy of the datafiles. To determine that you need to do a
move with the source/production database shutdown. Yeah, I know that can be
hard to schedule but it's necessary. If the copy won't start at that point then
Double Take is completely incompatible with Oracle and you can't go much
further. Now if that passes, allow Double Take to copy the production DB to the
backup server and while it's doing so check the hotbackup status of the database
using the following:

            SELECT COUNT(*)
            FROM DBA_DATA_FILES DF, SYS.V_$BACKUP B
            WHERE FILE_ID = FILE#
            AND DF.STATUS = 'AVAILABLE'
            AND B.STATUS = 'ACTIVE';

The number you get back should equal the number of datafiles in your database.
If it comes back as 0 then the database has not switched and the backup is
worthless. You may have to do this manually before running Double Take. Also
your production/source DB has to be in archive log mode or else hotbackup does
not work.

The reasons for this are wrapped around Oracle's "write as little as needed and
do so as seldomly as possible" idea. With this idea data block changes are not
sent to the datafiles until there is a need to. MicroSlop and Exchange work on
the exact opposite idea which makes them IO hogs, although Oracle can be the
same. In your case I would suspect that the hotbackup is the problem.

Dick Goulet

____________________Reply Separator____________________
Author: Denham Eva <[EMAIL PROTECTED]>
Date: 10/15/2002 7:08 AM

Thanks for the input so far. Double-Take works real time so the database is
never down.
I also followed their setup direction to the letter. Problem on our site is
that this product is being used for SQL Server and Exchange (Appears to work
fine there, but Oracle is a beast of another color compared to these "Access
on Steroids" databases), management are insisting for the sake of conformity
that this must work. At ever attempted startup another file gives an error,
most frustrating of all is that there is almost no consistency to the
errors.

Denham Eva

-----Original Message-----
Sent: Tuesday, October 15, 2002 4:04 PM
To: Multiple recipients of list ORACLE-L

Lewis,

I can understand where Eva is coming from. I had a demo of a similar
product some time ago. Their BIG selling point is that you have a
production
server and a backup that is close in time with your production server at
half
(or less) the cost of a hot standby. Their reasoning is that you don't have
Oracle running on the standby and consequently don't have to pay Oracle a
license fee for the second server since only one server is running at any
point
in time. Logically their point is well taken. Regrettably and
understandably
that is NOT Oracle's point of view.

Dick Goulet

____________________Reply Separator____________________

Author: Bishop Lewis <[EMAIL PROTECTED]>
Date: 10/15/2002 2:23 AM

I'm always dubious of these types of products (especially when there are no
reference sites available) and would opt for a batched up standby database
solution (syncing every 5/10/15 minutes or so) myself. I'm not saying
Double-Take is not good - I've got no experience of it and am sorry it's not
any help but you have an option should Double-Take not work correctly.

Lewis Bishop
---
Barclays Enable - ISS - E-NTRUST/Bexleyheath NT
Oracle Database Consultant
Watling Street, Bexleyheath, Kent, DA6 7RR (Mail Van R)
Phone : 020 8298 3418
Mobile: 07950 380857
Email : [EMAIL PROTECTED]
"Enabling Competitive Advantage for Barclays in IT and Business Processing"

-----Original Message-----
Sent: 15 October 2002 08:28
To: Multiple recipients of list ORACLE-L

This header confirms that this email message has been swept for the
presence of computer viruses.

Corporate IT
THE WOOLWICH
----------------------------------------------------------------------
Hello Esteemed Gurus
Pls advise.......
We are trying to get Double Take to work on our site. Does anyone actually
have this product working???
Salesperson claims Double Take is certified by Oracle - does anyone know?
Where could I find out, other than the company itself?
For those of you who don't know this product pls give your opinion. Double
Take is a software that copies your database files and parameter files etc
across to a disaster recovery machine, bit for bit. At failure of the
production the recovery becomes the production system and starts up the
database. Basicly the datafiles are still open??
We get the following error when we start up the database on the recovery
system in tests:
ORA-01172: recovery of thread 1 stuck at bloack 176624 of file 2.
I would just like to add that when this happens we resync the databases and
try again to test and guess what - it is the turn of file 3 to give the
above error, and so back and forth we go.
To say the very least I am frustrated beyond comprihension. To make this
worse there is no one else in South Africa that uses this software with
Oracle, apparently in France. Convienant - I'd say. So I have no one to turn
to about this. (Apparently it works well with MSSQL). Anyone any ideas?
The Enviroment is Windows 2K SP3.
Oracle 817
Regards
Denham Eva
Oracle DBA
"UNIX is basically a simple operating system, but you have to be a genius to
understand the simplicity."
Dennis Ritchie.

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<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
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<TITLE>RE: RE: Double Take and Oracle</TITLE>
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Thanks for the input so far. Double-Take works real time so the
database is never down.
 I also followed their setup direction to the letter. Problem on
our site is that this product is being used for SQL Server and Exchange (Appears
to work fine there, but Oracle is a beast of another color compared to these
"Access on Steroids" databases), management are insisting for the sake
of conformity that this must work. At ever attempted startup another file gives
an error, most frustrating of all is that there is almost no consistency to the
errors.

Denham Eva

-----Original Message-----
 From: [EMAIL PROTECTED] [<A
HREF=""mailto:[EMAIL PROTECTED]">mailto:[EMAIL PROTECTED]</A>]
 Sent: Tuesday, October 15, 2002 4:04 PM
 To: Multiple recipients of list ORACLE-L
 Subject: Re:RE: Double Take and Oracle

Lewis,

I can understand where Eva is coming
from.  I had a demo of a similar
 product some time ago.  Their BIG selling point is that
you have a production
 server and a backup that is close in time with your production
server at half
 (or less) the cost of a hot standby.  Their reasoning is
that you don't have
 Oracle running on the standby and consequently don't have to
pay Oracle a
 license fee for the second server since only one server is
running at any point
 in time.  Logically their point is well taken. 
Regrettably and understandably
 that is NOT Oracle's point of view.

Dick Goulet

____________________Reply Separator____________________

Author: Bishop Lewis <[EMAIL PROTECTED]>
 Date:       10/15/2002 2:23
AM

I'm always dubious of these types of products (especially when
there are no
 reference sites available) and would opt for a batched up
standby database
 solution (syncing every 5/10/15 minutes or so) myself. I'm not
saying
 Double-Take is not good - I've got no experience of it and am
sorry it's not
 any help but you have an option should Double-Take not work
correctly.

Lewis Bishop
 ---
 Barclays Enable - ISS - E-NTRUST/Bexleyheath NT
 Oracle Database Consultant
 Watling Street, Bexleyheath, Kent, DA6 7RR (Mail Van R)
 Phone : 020 8298 3418
 Mobile: 07950 380857
 Email : [EMAIL PROTECTED]
 "Enabling Competitive Advantage for Barclays in IT and
Business Processing"
 
 -----Original Message-----
 Sent: 15 October 2002 08:28
 To: Multiple recipients of list ORACLE-L

This header confirms that this email message has been swept for
the
 presence of computer viruses.

Corporate IT
 THE WOOLWICH
 ----------------------------------------------------------------------</F
ONT>
 Hello Esteemed Gurus 
 Pls advise....... 
 We are trying to get Double Take to work on our site. Does
anyone actually
 have this product working??? 
 Salesperson claims Double Take is certified by Oracle - does
anyone know?
 Where could I find out, other than the company itself?
 For those of you who don't know this product pls give your
opinion. Double
 Take is a software that copies your database files and
parameter files etc
 across to a disaster recovery machine, bit for bit. At failure
of the
 production the recovery becomes the production system and
starts up the
 database. Basicly the datafiles are still open??
 We get the following error when we start up the database on the
recovery
 system in tests: 
 ORA-01172: recovery of thread 1 stuck at bloack 176624 of file
2. 
 I would just like to add that when this happens we resync the
databases and
 try again to test and guess what - it is the turn of file 3 to
give the
 above error, and so back and forth we go.
 To say the very least I am frustrated beyond comprihension. To
make this
 worse there is no one else in South Africa that uses this
software with
 Oracle, apparently in France. Convienant - I'd say. So I have
no one to turn
 to about this. (Apparently it works well with MSSQL). Anyone
any ideas?
 The Enviroment is Windows 2K SP3. 
 Oracle 817 
 Regards 
 Denham Eva 
 Oracle DBA 
 "UNIX is basically a simple operating system, but you have
to be a genius to
 understand the simplicity." 
 Dennis Ritchie.

DISCLAIMER 
 This message is for the named person's use only. It may
contain
 confidential, proprietary or legally privileged information.
No
 confidentiality or privilege is waived or lost by any
mistransmission. If
 you receive this message in error, please immediately delete it
and all
 copies of it from your system, destroy any hard copies of it
and notify the
 sender. You must not, directly or indirectly, use, disclose,
distribute,
 print, or copy any part of this message if you are not the
intended
 recipient. TFMC, its holding company, and any of its
subsidiaries each
 reserve the right to monitor and manage all e-mail
communications through
 its networks. 
 Any views expressed in this message are those of the individual
sender,
 except where the message states otherwise and the sender is
authorized to
 state them to be views of any such entity.

This e-mail message has been scanned for Viruses and Content and
cleared by
 MailMarshal - For more information please visit
www.marshalsoftware.com

-- 
 Please see the official ORACLE-L FAQ: <A
HREF=""http://www.orafaq.com" TARGET="_blank">http://www.orafaq.com</A>
 -- 
 Author: Bishop Lewis
   INET: [EMAIL PROTECTED]

Fat City Network Services    -- 858-538-5051 <A
HREF=""http://www.fatcity.com" TARGET="_blank">http://www.fatcity.com</A>
 San Diego, California       
-- Mailing list and web hosting services
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NT>
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ORACLE-L
 (or the name of mailing list you want to be removed
from).  You may
 also send the HELP command for other information (like
subscribing).

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 -- 
 Author: 
   INET: [EMAIL PROTECTED]

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RE: RE: RE: Double Take and Oracle

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