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Home -> Community -> Mailing Lists -> Oracle-L -> RE: duplexing redos and archives
I've never personally had to deal with #2, nor have I heard of anyone
experiencing this particular situation. In fact, I hope never to be able to
say I had to deal with a logically corrupt redo log. I unfortunately have
dealt with corrupted archive logs and the long hours spent rebuilding a db
have made me very, very protective of my redo. Compare the cost of 1g of
space in a 500g array against an unrecoverable db.
However, if the redo logs are written using different hardware paths, it is possible to have 1 with an untrapped corruption while the other is okay. Again this is theory...
I recently encountered a situation where duplexing saved my behind. On a non-prod system, we reconfigured the disks. Prior to shutdown, I moved some the redo logs off of the disks that were going away. A miscommunication resulted in the SA starting the dbs before I had a chance to rename the redo logs. Since I was duplexing (they are mirrored at the hardware level as well), the database started (tossed a couple of errors in the alert log) without problem. When I finally realized what had happened, I simply dropped and recreated the log groups (needed to resize them anyway...) with no additional downtime.
Dan
-----Original Message-----
Sent: Tuesday, August 06, 2002 4:29 PM
To: Multiple recipients of list ORACLE-L
Has anyone ever heard of #2 ever occuring? Even if possible I am not aware of anyone presenting a clear case of this actually happening.
Ethan Post
(972) 577-6552
Ethan.Post_at_ps.net
perotdba (AIM), epost1 (Yahoo)
-----Original Message-----
Sent: Tuesday, August 06, 2002 4:08 PM
To: Multiple recipients of list ORACLE-L
I think the logical argument is on your side as well. The Oracle kernel has some code path that allows it to write different things into supposedly "identical" redo logs, to account for device glitches, etc. But this works only if you use the *Oracle* capability to multiplex redo.
Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
Upcoming events:
- Hotsos Clinic, Oct 1-3 San Francisco, Oct 15-17 Dallas, Dec 9-11
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-----Original Message-----
Sent: Tuesday, August 06, 2002 1:44 PM
To: Multiple recipients of list ORACLE-L
This may be 'old school' thinking, but I prefer to duplex my redo logs.
Why?
Because there are some things that mirroring cannot protect you against.
1. The deletion of a redo log through human error (been there, recovered
from it...)
2. The logical corruption of a redo log (never experienced it myself,
but it
is theortically possible)
3. Oracle's fault tolerance regarding the ability to function as long as
1
redo log in a group is accessible
Considering the critical nature of the redo logs (lose one and your
recovery
is done...and perhaps your job) and their small size in relation to
overall
databse size, duplexing in a group makes sense.
This is one of those issues where valid arguements exist on both sides.
In
some ways, the logical arguements are on the side of not duplexing redo
logs
that are mirrored. However, when you consider that the loss or
corruption of
a single redo log can cause the database to be unrecoverable is enough
to
justify the cost of duplexing.
Just my humble (old school) opinion
Dan Fink
-----Original Message-----
Sent: Tuesday, August 06, 2002 12:13 PM
To: Multiple recipients of list ORACLE-L
Currently we are duplexing our redo logs and archive logs through oracle. We do this at the oracle level because we are using mirroring (raid0?) and if we lose a redo log or archive file the database will not be affected.
We will be moving to raid5 arrays in the future and are wondering whether we still need to do the duplexing. Since the arrays are made up of data disks plus a parity disk plus a hot swap do we need to worry about losing a redo log? Our sys admins are telling us we don't and I tend to agree with them but we want to get other opinions on the subject.
How are shops handling this who are using raid5?
Thanks.
Joe
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Author: Joe Armstrong-Champ
INET: Joseph.Armstrong-Champ_at_tufts.edu
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Author: Cary Millsap
INET: cary.millsap_at_hotsos.com
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Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists --------------------------------------------------------------------To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists --------------------------------------------------------------------To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). Received on Tue Aug 06 2002 - 18:29:51 CDT
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