Re: ASM is single point of failure ?
- From: Tanel Põder <tanel.poder.003@xxxxxxx>
- To: <gogala@xxxxxxxxxxxxx>, <kevinc@xxxxxxxxxxxxx>
- Date: Tue, 9 May 2006 22:09:13 +0800
My biggest problem with it is the fact that I cannot
backup my data by anything else but RMAN. With all due
respect, I don't trust Oracle that much. I want to see
files and the space allocation. Black box approach doesn't
work very well for me. As a pessimist, I know that a coffin
is also a black box.
Yeah, that was the first thing that came into my mind when Oracle started
marketing ASM.
I've recommended my customers to keep their redologs and archivelogs outside
ASM if their data is precious to them. Btw, It's the redo stream which we
have to protect the most, not the datafiles alone. As long as you've got
full redo stream available, it doesn't matter how many weeks old backup you
take to get your data back.
Anyway, for the customers stuck on ASM with Standard Ed RAC, I once wrote an
experimental utility which can dump out their online redologs from physical
ASM files. You just have to extract the redolog (or any datafile) allocation
unit locations when ASM instance is running - you can do the dump without
any instance available later on as long as you haven't changed the file
locations or sizes.
The script itself is very simple, thanks to cached ASM allocation unit info
availability from X$KFFXP and that the script doesn't account for all ASM
nuisances as rebalancing, mirroring, possible non-default allocation unit
and stripe sizes etc..
select
'dd if='|| d.path||' bs=1048576 skip='||AU_KFFXP||' count=1 '||
'>> /tmp/'||substr('&1',instr('&1','/',-1)+1)||'.dmp' cmd
from
X$KFFXP X, V$ASM_DISK D, V$ASM_ALIAS A
where
lower(A.NAME) = lower(substr('&1',instr('&1','/',-1)+1))
and X.NUMBER_KFFXP = A.FILE_NUMBER
and X.GROUP_KFFXP = A.GROUP_NUMBER
and X.INCARN_KFFXP = A.FILE_INCARNATION
and X.DISK_KFFXP = D.DISK_NUMBER
and X.GROUP_KFFXP = D.GROUP_NUMBER
order by
X.XNUM_KFFXP;
http://www.integrid.info/asmdump.sql
http://www.integrid.info/asmdumpf.sql
Highly experimental of course, don't rely your recovery strategy on it ;)
Tanel.
[new website coming soon ;]
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