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Re: OS Level Defrag

From: <Brian_P_MacLean_at_eFunds.Com>
Date: Fri, 28 Nov 2003 07:44:25 -0800
Message-ID: <>

Sorry can't help with the "when did it happened" question.

But in defense of the SysAdmin, I have seen the benefits of defraging on both Unix and NT.

In the NT case the defraging was caused by lots of small fragments caused by the datafile being auto extended in short increments, and that being mixed on the same file system with other file updates/additions/deletes.

In the Unix case, I was doing a lot of restores to a testing system. When I did the restores I had 5 or 6 uncompress commands outputting to the same /u mount point. After doing this my wio times when through the roof. On the next restore I restricted my restore to one uncompress at a time to each of my /u mount points ... the wio problem went away.

The last point I'd like to make is "trust no one" with your data. Always sum and/or cksum files before and after moving them around (there are gnu versions of these commands for non Unix systems). And 3 last words - backup backup backup.

                      "Sujatha Madan"                                                                                              
                      <Sujatha.Madan_at_op        To:       Multiple recipients of list ORACLE-L <>               
            >              cc:                                                                                 
                      Sent by:                 Subject:  OS Level Defrag                                                           
                      11/27/2003 06:59                                                                                             
                      Please respond to                                                                                            


Does anyone here do an O/S level defrag of their Oracle filesystems???

Background: (Tru64/

Sysadmin here were adamant that the Oracle domains were running out of extents and were highly fragmented (O/S level). DBA was adamant that the Oracle filesystems should not be defragmented. I lost the battle and the sysadmins are defragging the domains.

I now have a corruption on a table partition with 100 million plus rows on a 50G datafile. I am wondering if the defrag has caused this corruption.

The only way I can think of finding out is:

Finding the approx date of the corruption using the query SELECT ROWID, <LAST_COLUMN_OF_TABLE> from <TABLE_NAME(PARTITION)>;
(which will do the full tablescan row by row).

And then finding when the defrag utility was hitting the particular datafile that is corrupted.

But this reasoning is flawed ....

Does anyone have another method of trying to pinpoint if the O/S defrag caused the corruption????



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Received on Fri Nov 28 2003 - 09:44:25 CST

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