Re: ASM is single point of failure ?

From: Tanel Põder <tanel.poder.003_at_mail.ee>
Date: Tue, 9 May 2006 22:09:13 +0800
Message-ID: <088001c67372$2b8a2ea0$3f121eac@porgand>

> 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 ;]

--
http://www.freelists.org/webpage/oracle-l

Received on Tue May 09 2006 - 09:09:13 CDT