RE: ZFS snapshots

  • From: Hemant K Chitale <hkchital@xxxxxxxxxxxxxx>
  • To: "Donahue, Adam" <Adam.Donahue@xxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
  • Date: Wed, 13 Dec 2006 00:05:06 +0800


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@xxxxxxxxxxxxxx]
Sent: Tuesday, December 12, 2006 10:20 AM
To: Donahue, Adam; oracle-l@xxxxxxxxxxxxx
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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