Glenn ,
even though everything are mirrored , splitting is not
instantaneous. When track or block level splitting ( I
don't know EMC uses which one. I know Hitachi uses
track level splitting ) takes place what happens to
the committed transaction which is being flushed to
that very same track or tracks....? Only half of the
info would be in the split copy. Thats why such copies
are said to be in 'inconsistent state'. Neither ORACLE
nor software responsible for split knows what pieces
are missing. To bring those pieces back you got to
merge teh BCV again. So the safest way of creating a
copy is to place the tablespaces in hot backup mode.
I assume you are quiet familier with Hot backup mode
so I won't go in detail but suffice it to say that in
the present case the missing pieces are in the log
file which should be archived at the end of hot backup
and safed off with the backup for recovery purpises.
When you recover the database in the BCV you have to
apply the archived log file and thus you are supplying
the missing piece.
Hope this helps.
Regards,
RS
--- Glenn Travis <Glenn.Travis_at_sas.com> wrote:
> Well, yeah. But why is it inconsistent? Please
> provide details. As you are with EMC, do you have
> any papers which discuss at that level? (not the
> process steps, I have those. but why?)
>
> I know that if only the datafiles are mirrored, then
> yes, you must use hot backup as the redo changes
> need to be written in full Oracle blocks. But what
> if everything (datafiles, redo, control, archive)
> are all in the mirrored set? How would anything get
> inconsistent by breaking a mirror?
>
> -----Original Message-----
> Sent: Monday, September 24, 2001 4:19 PM
> To: Glenn.Travis_at_sas.com; oracledba_at_lazydba.com
>
>
>
> The reason for split is to get a consistent data
> -----Original Message-----
> Sent: Monday, September 24, 2001 12:41 PM
> To: LazyDBA.com Discussion
>
>
> It is my understanding that the common
> implementation of copying an Oracle
> database on an EMC using BCVs is this;
>
> 1) put the source database in BEGIN BACKUP mode for
> all the tablespaces,
> 2) break the mirror,
> 3) put tablespaces in END BACKUP mode
> 4) recover on target, or backup the files.
>
> Question:
> Why is it necessary to put the database in 'hot
> backup' mode when splitting
> a BCV? If it is just like splitting a mirror, why
> do you need the database
> in hot backup mode at all? Wouldn't it be the same
> as losing one side of a
> mirrored pair? When that happens, no extra
> processing is needed.
>
>
>
>
>
>
> --------
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> Author: Glenn Travis
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Received on Mon Sep 24 2001 - 15:47:16 CDT
