RE: Oracle DB Backups on SAN with ALTER SYSTEM SUSPEND

Mike,

I, too, was thinking that the Snapshot or split operation was not atomic and requires
a suspension of I/O. However, [see my other posting to Oracle-L], I now believe that
Jeremiah is right and that a SUSPEND should not be necessary for the datafiles. Reading postings on MetaLink and reading "between the lines" in the Oracle documentation,
it may be the case that some implementations of splitting-mirrors may not work unless I/O is really suspended and that is why Oracle offers the SUSPEND option.
EMC and Hitachi do not seem to require a SUSPEND.

As for the controlfile, since an ALTER TABLESPACE BEGIN BACKUP doesn't really stop updates to the controlfile, and an OS copy of the controlfile might be "inconsistent" to Oracle, a binary backup would become necessary. The datafile backup by the OS is "inconsistent" but not fuzzy as the ALTER TABLESPACE BEGIN
BACKUP command has been issued so Oracle decides to apply archive logs.

Hemant

At 10:39 AM 26-03-03 -0800, you wrote:
>Jeremiah,
>The only reason I could forsee is if the split is not atomic. This is the
>case
>in our (Non-SAN) environment. The split takes several minutes and the
>control
>files have been mis-matched when the DB copy was started on the reporting
>server.
>My solution under V8.0 was to use only one of the control files for
>reporting
>database.
>
>My $0.02
>Mike Hand
>
>-----Original Message-----
>Sent: Wednesday, March 26, 2003 11:04 AM
>To: Multiple recipients of list ORACLE-L
>
>
>Why do you have to suspend?
>
>--
>Jeremiah Wilton
>http://www.speakeasy.net/~jwilton
>
>On Wed, 26 Mar 2003, Hemant K Chitale wrote:
>
> >
> > We want true server-less backups. I know that RMAN's overhead is [much]
>lower
> > than that of the ALTER TABLESPACE BEGIN/END BACKUP but the
> > Snapshot method in a SAN [akin to splitting and resilivering a mirror, in
> > some ways]
> > should be much faster. The database is in BACKUP mode only for the time
>it
> > takes the SAN to create the Snapshot which, I've been told, is seconds or
> > minutes,
> > irrespective of the size of the database. [Of course, there will be some
> > time lag
> > between the first ALTER TABLESPACE <tbs> BEGIN BACKUP and the
> > ALTER SYSTEM SUSPEND command when the database will be doing a
> > Checkpoint at each Tablespace, and writing more Redo for transactions upto
> > the ALTER SYSTEM SUSPEND and will the END BACKUPs are still being issued.]
> >
> > And I cannot use RMAN with the Snapshot method. I must SUSPEND the
>database
> > and RMAN does not support that.
> >
> > See
> >
>http://download-west.oracle.com/docs/cd/A87860_01/doc/server.817/a76993/osba
>ckup.htm#4233
> > "Making Backups in Suspend Mode" in Chapter 4 "Performing Operating
>System
> > Backups"
> > of the 8i Backup and Recovery Guide.
> >
> > Hemant
> >
> > At 05:38 AM 26-03-03 -0800, you wrote:
> > >Hemant - If you've got to rework your backup script anyway (and retest
>it),
> > >why not consider switching to RMAN at this time? In my experience,
> > >negligible interference with production during a hot backup.
> > >
> > >Dennis Williams
> > >DBA, 40%OCP, 100% DBA
> > >Lifetouch, Inc.
> > >dwilliams_at_lifetouch.com
> > >
> > >
> > >-----Original Message-----
> > >Sent: Tuesday, March 25, 2003 10:49 PM
> > >To: Multiple recipients of list ORACLE-L
> > >
> > >
> > >
> > >Some of my databases will be migrating to a SAN.
> > >Currently, I run hot backups to disk using the
> > >ALTER TABLESPACE <tbs> BEGIN BACKUP ;
> > >host cp <file> <target>;
> > >ALTER TABLESPACE <tbs> END BACKUP
> > >
> > >On a SAN, where the vendor promises server-less backups
> > >using Snapshots, I guess I would have to issue the
> > >commands :
> > >ALTER TABLESPACE <tbs1> BEGIN BACKUP
> > >..
> > >..
> > >ALTER TABLESPACE <tbsN> BEGIN BACKUP
> > >
> > >ALTER SYSTEM SUSPEND
> > >....> take a "snapshot"
> > >ALTER SYSTEM RESUME
> > >
> > >ALTER TABLESPACE <tbs1> END BACKUP
> > >..
> > >..
> > >ALTER TABLESPACE <tbsN> END BACKUP
> > >
> > >
> > >Would that be right ? What are real-world experiences
> > >[bugs / time required for the SUSPEND/RESUME, actually
> > >flushing all I/O to the disks] ?
> > >
> > >The SAN will be a Hitachi 9970 sold by Sun.
> > >The databases will be 8.1.7 32-bit / 64-bit on Solaris 8.
> > >
> > >Hemant K Chitale
> > >http://hkchital.tripod.com
> > >--
> > >Please see the official ORACLE-L FAQ: http://www.orafaq.net
> > >--
> > >Author: Hemant K Chitale
> > > INET: hkchital_at_singnet.com.sg
> > >
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> > >Author: DENNIS WILLIAMS
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> > Hemant K Chitale
> > My personal web site is : http://hkchital.tripod.com
> >
> >
> > --
> > Please see the official ORACLE-L FAQ: http://www.orafaq.net
> > --
> > Author: Hemant K Chitale
> > INET: hkchital_at_singnet.com.sg
> >
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>--
>Please see the official ORACLE-L FAQ: http://www.orafaq.net
>--
>Author: Jeremiah Wilton
> INET: jwilton_at_speakeasy.net
>
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>Author: Hand, Michael T
> INET: HANDM_at_polaroid.com
>
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Hemant K Chitale
My personal web site is : http://hkchital.tripod.com

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Hemant K Chitale
  INET: hkchital_at_singnet.com.sg

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