RE: ZFS snapshots
- From: "Donahue, Adam" <Adam.Donahue@xxxxxxxxx>
- To: "Kerber, Andrew" <Andrew.Kerber@xxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 12 Dec 2006 09:58:38 -0500
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
________________________________
From: Kerber, Andrew [mailto:Andrew.Kerber@xxxxxxx]
Sent: Tuesday, December 12, 2006 9:32 AM
To: Donahue, Adam; oracle-l@xxxxxxxxxxxxx
Subject: RE: ZFS snapshots
Your problem will probably be matching up the Oracle scn's. They change
rapidly, and if they don't match Oracle will give you the old need media
recovery message. I am not sure if you can copy them quick enough to
keep all the Oracle scn's in sync. I know it can be done with the DB
down, but I wouldn't count on doing it with the DB up.
Andrew W. Kerber
Oracle DBA
UMB
816-860-3921
andrew.kerber@xxxxxxx
"If at first you dont succeed, dont take up skydiving"
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Donahue, Adam
Sent: Tuesday, December 12, 2006 8:18 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: ZFS snapshots
Folks,
Sanity check question for those familiar with ZFS.
Is there any reason, assuming all datafiles were on a single ZFS
filesystem (which is the level of consistent snapshot granularity), that
something like the following wouldn't work to copy a database (and
refresh on a regular basis) -
zfs snapshot data@n
zfs snapshot log@n
zfs send -i data@n-1 data@tag | rsh target zfs receive data
zfs send -i log@n-1 data@tag | rsh target zfs receive log
zfs clone data@n data-qa
zfs clone log@n log-qa
- all with the database online and running without any instance
downtime?
Given the granularity of writes to the redo logs, I'm trying to think of
how corruption might be introduced here, if it could. From what I see
above, though, it would be more-or-less like a straight-forward database
crash - which would on the target side would be recovered automatically
during instance startup.
Adam
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