Jeremiah / Deborah,
My understanding is/was that the Snapshot creation wasn't atomic -- it can take "a little bit of time"
and, therefore, it becomes necessary to suspend I/O.
Now, I haven't had a chance yet to speak to the Sun/Hitachi engineers and I am going
by what management has understood and conveyed to me -- that the database must
be "quiesced". Hopefully, next week, I will be allowed to speak to the engineers before
they set up the SAN.
Reading Oracle's documentation in the Backup and Recovery guide
"Using the Oracle8i SUSPEND/RESUME functionality, you can suspend I/O to the database, then split the mirror and make a backup of the split mirror. This feature, which complements the hot backup functionality, allows you to quiesce the database so that no new I/O can be performed. You can then access the suspended database to make backups without I/O interference.
Note: Some RAID devices benefit from suspending writes while the split operation is occurring; your RAID vendor can advise you on whether your system would benefit from this feature.
"
and
"After a successful database suspension, you can back up the database to disk or break the mirrors. Because suspending a database does not guarantee immediate termination of I/O, Oracle recommends that you precede the SUSPEND statement with a BEGIN BACKUP statement to place the tablespaces in hot backup mode.
You must use conventional operating system backup methods to back up split mirrors. RMAN cannot make database backups or copies because these operations require reading the datafile headers. After the database backup is finished or the mirrors are re-silvered, then you can resume normal database operations using the RESUME statement.
Backing up a suspended database without splitting mirrors can cause an extended database outage because the database is inaccessible during this time. If backups are taken by splitting mirrors, however, then the outage is nominal. The outage time depends on the size of cache to flush, the number of datafiles, and the time required to break the mirror
"
I did get the impression that a SUSPEND was necessary.
However, I have read a Hitachi document at http://www.hds.com/pdf/ods.pdf and I think that a SUSPEND is not mandatory.
I will come back to the list when I get more information from the Sun/Hitachi engineers and see the scripts/script-templates that they will be providing.
Hemant
At 08:04 AM 26-03-03 -0800, you wrote:
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/osbackup.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.
> >[EMAIL PROTECTED]
> >
> >
> >-----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: [EMAIL PROTECTED]
> >
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> Hemant K Chitale
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>
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: Hemant K Chitale
> INET: [EMAIL PROTECTED]
>
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-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Jeremiah Wilton INET: [EMAIL PROTECTED]
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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: [EMAIL PROTECTED]
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