Message-Id: <7.0.1.0.0.20061213000318.01ba7db0@singnet.com.sg>
Date: Wed, 13 Dec 2006 00:05:06 +0800
To: "Donahue, Adam" <Adam.Donahue@kbcfp.com>, <oracle-l@freelists.org>
From: Hemant K Chitale <hkchital@singnet.com.sg>
Subject: RE: ZFS snapshots
In-Reply-To: <248A58C2AB63304C82F0706DE62FB345015AA2A3@nyc.kbcfp.com>
References: <248A58C2AB63304C82F0706DE62FB345015AA2A3@nyc.kbcfp.com>
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Reply-to: hkchital@singnet.com.sg


My contention is that ArchiveLog streams allow you PITR to any point in time.

If you take a snapshot you can only do an Instance Recovery to the
point of the snapshot -- ie it would be like simulating a server failure
and you restarting the database whereby it  does a "Crash Recovery"
because the datafiles were fuzzy (not in backup mode).

Hemant

At 11:27 PM Tuesday, Donahue, Adam wrote:
>I replied privately, but I don't think this step is strictly necessary -
>nor desired, as we'd then lose our ability to perform PITR to any SCN
>within the backup window, no?
>
>Adam
>
>-----Original Message-----
>From: Hemant K Chitale [mailto:hkchital@singnet.com.sg]
>Sent: Tuesday, December 12, 2006 10:20 AM
>To: Donahue, Adam; oracle-l@freelists.org
>Subject: RE: ZFS snapshots
>
>
>You would still be recommended to run
>ALTER TABLESPACE (DATABASE in 10g)  BEGIN BACKUP .. before you take
>the Snapshot
>and
>ALTER TABLESPACE (DATABASE) END BACKUP  followed by ALTER SYSTEM
>ARCHIVE LOG CURRENT  after the Snapshot.
>
>Hemant
>
>
>At 10:58 PM Tuesday, Donahue, Adam wrote:
> >Well, a ZFS snapshot is atomic - meaning, it's not like copying a
> >datafile in that it doesn't read things block-by-block, meaning the
> >file can change underneath you while you copy it.  Instead, because
> >of the way ZFS works, it merely marks an existing "uberblock" to be
> >preserved, which is a single, atomic state of the filesystem as of a
> >given time.
> >
> >I admit it's not clean - even if it works.  But I'm curious if I'm
> >missing something that would make it not work at all in some cases.
> >
> >Adam
>
>
>Hemant K Chitale
>http://web.singnet.com.sg/~hkchital
>
>
>
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Hemant K Chitale
http://web.singnet.com.sg/~hkchital


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