Restore and Recover Fuzzy datafiles

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Restore and Recover Fuzzy datafiles

Restore and Recover Fuzzy datafiles

2006-05-25 - By Mark W. Farnham

Reply: 1 2 3 4 5 6 7 8

Assumption: By fuzzy you mean a datafile that was copied by an operating
system utility without the tablespace being put in backup mode so that first
changes to blocks after the beginning of backup have not been redo logged as
the whole block.

If that is what you mean, then yes.

If the particular file was simply not written to during the operating system
copy such that there are no ?fractured blocks? then the recovery can be made
by telling the database to end backup.

That?s no way to run the railroad, but you might get lucky. Verifying that
you actually did get lucky is usually done by making sure that block
checking is on and running an export of everything in the tablespace.

If you get an invalid block and if you have a different backup and the
thread of relevant redo logs, and a utility that will allow you to replace
the set of sectors that make up an Oracle block from one file to another, it
is possible to replace invalid blocks with valid blocks. Of course this is a
statistical game and you if the file contains blocks that are chronically
?write hot? during the time the invalid backups are taken, the odds are
skewed against you.

Before you could tell the database to ?end? backup, you also had to patch
the beginning and ending blocks of the file (lie to Oracle) so that Oracle
did not consider the file to be ?fuzzy,? but I doubt you?re working with a
vintage of the Oracle software that old. If you are, you?ll need some kind
of binary block editor.

All results of such attempts should be looked at with a jaundiced eye in
terms of future supportability.

Also, if you must mix ?fuzzy? backups of the same file to get all
?unfractured? blocks, it is far easier to recover the oldest version of the
file (again with the assumption that you have the full thread of redo logs)
with any required ?fractured? blocks in the oldest file replaced with
younger versions of the block.

I hope I answered your question. Maybe someone else on the list knows a
better way to proceed, and given precise information about your system,
Oracle vintage and all that someone may have better options for you. All the
risks of whether you actually made it work and the suitability of using any
resulting data for any purpose are the liability of someone other than me or
my company. (probably yours.)

Regards,

mwf

-- --Original Message-- --
From: oracle-l-bounce@(protected) [mailto:oracle-l-bounce@(protected)]On
Behalf Of Sinardy Xing
Sent: Thursday, May 25, 2006 2:00 AM
To: Oracle-L Freelists
Subject: Restore and Recover Fuzzy datafiles

Hi Guys,

Have you ever restore and try to recover fuzzy datafiles?

--
Kind regards,

Sinardy

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Assumption:
By fuzzy you mean a datafile that was copied by an operating system utility
without the tablespace being put in backup mode so that first changes to blocks
after the beginning of backup have not been redo logged as the whole block.<o:p
></o:p>


<![if
!supportEmptyParas]> <![endif]><o:p></o:p>


If that is
what you mean, then yes.<o:p></o:p>


<![if
!supportEmptyParas]> <![endif]><o:p></o:p>


If the
particular file was simply not written to during the operating system copy such
that there are no “fractured blocks” then the recovery can be made
by telling
the database to end backup.<o:p></o:p>


<![if
!supportEmptyParas]> <![endif]><o:p></o:p>


That&#8217
;s no
way to run the railroad, but you might get lucky. Verifying that you actually
did get lucky is usually done by making sure that block checking is on and
running an export of everything in the tablespace.<o:p></o:p>


<![if
!supportEmptyParas]> <![endif]><o:p></o:p>


If you get
an invalid block and if you have a different backup and the thread of relevant
redo logs, and a utility that will allow you to replace the set of sectors that
make up an Oracle block from one file to another, it is possible to replace
invalid blocks with valid blocks. Of course this is a statistical game and you
if the file contains blocks that are chronically “write hot” during
the time
the invalid backups are taken, the odds are skewed against you.<o:p></o:p>


<![if
!supportEmptyParas]> <![endif]><o:p></o:p>


Before you
could tell the database to “end” backup, you also had to patch the
beginning
and ending blocks of the file (lie to Oracle) so that Oracle did not consider
the
file to be “fuzzy,” but I doubt you’re working with a vintage
of the Oracle
software that old. If you are, you’ll need some kind of binary block
editor.<o:p></o:p>


<![if
!supportEmptyParas]> <![endif]><o:p></o:p>


All
results of such attempts should be looked at with a jaundiced eye in terms of
future
supportability.<o:p></o:p>


<![if
!supportEmptyParas]> <![endif]><o:p></o:p>


Also, if
you must mix “fuzzy” backups of the same file to get all &#8220
;unfractured” blocks,
it is far easier to recover the oldest version of the file (again with the
assumption that you have the full thread of redo logs) with any required &#8220
;fractured”
blocks in the oldest file replaced with younger versions of the block.<o:p></o
:p>


<![if
!supportEmptyParas]> <![endif]><o:p></o:p>


I hope I
answered your question. Maybe someone else on the list knows a better way to
proceed, and given precise information about your system, Oracle vintage and
all that someone may have better options for you. All the risks of whether you
actually made it work and the suitability of using any resulting data for any
purpose are the liability of someone other than me or my company. (probably
yours.)<o:p></o:p>


<![if
!supportEmptyParas]> <![endif]><o:p></o:p>


Regards,<o
:p></o:p>


<![if
!supportEmptyParas]> <![endif]><o:p></o:p>


mwf<o:p><
/o:p>


<![if
!supportEmptyParas]> <![endif]><o:p></o:p>

----
-Original
Message-- -- 
From:
oracle-l-bounce@(protected) [mailto:oracle-l-bounce@(protected)]On Behalf Of Sinardy Xing 
Sent: Thursday, May 25, 2006 2:00
AM 
To: Oracle-L Freelists 
Subject: Restore and Recover Fuzzy
datafiles

<![if !supportEmptyParas]> <![endif]><o:p></o:p>

Hi Guys,<o:p></o:p>

 
<o:p></o:p>

Have you ever
restore and try to recover fuzzy datafiles?<o:p></o:p>

 
<o:p></o:p>

 
-- 
Kind regards, 
 
Sinardy <o:p></o:p>

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