Re: OH YEAH - switching raw device to fs

From: Noons <wizofoz2k_at_yahoo.com.au>
Date: 16 Sep 2004 18:03:52 -0700
Message-ID: <73e20c6c.0409161703.4910b1e9@posting.google.com>

Igor <igor.news_at_merkudelete.org> wrote in message news:<pan.2004.09.16.15.20.38.126417_at_merkudelete.org>...
> [SECOND STEP]
> Now I have an database on file system, right?
> So, what I will do, tomorrow (I hear your yawns, sorry, but my kids are
> waiting), is, to back up the open fs database to raw device via dd.
> Just a few lines of commands, isn't it ...
>
> Of course, now I have to understand how to let dd skip first 4096 in
> output, so that dd does not overwrite the LVCB. But this is for tomorrow.

ah yes, the funny AIX LVM header. Here is the doco straight from "man dd":
dd [ bs=BlockSize ][ cbs=BlockSize ] [ conv= [ ascii | block | ebcdic | ibm | unblock ] [ lcase | ucase ] [ iblock ] [ noerror ] [ swab ] [ sync ] [ oblock ] [ notrunc ] ] [ count=InputBlocks ] [ files=InputFiles ] [ fskip=SkipEOFs ] [ ibs=InputBlockSize ] [ if=InFile ] [ obs=OutputBlockSize ][ of=OutFile ] [ seek=RecordNumber ] [ skip=SkipInputBlocks ][ span=yes|no ]

See that little "seek=RecordNumber"? That's what you want. Make sure the "obs" is at least as big as what you want to skip. And it should work if you set seek=1. Ie, the seek has to "move forward" the amount you want expressed in terms of the obs.

Something like this:
dd if=/cooked/file.dbf of=/raw/devwhatever obs=4096 seek=1 and Roberto should be your uncle.

But don't take this for granted: try it out with some text files in a normal login in AIX and see what I mean. Try for example to use dd to append a file to another. It works. At least it does in my AIX:
-rwxrwxrwx 1 oracle dba 65065 Sep 16 12:10 cleanDB.sql* /home/oracle/Scripts$ dd if=cleanDB.sql of=zot.sql 127+1 records in.

-rwxrwxrwx   1 oracle   dba           65065 Sep 16 12:10 cleanDB.sql*
-rw-r--r--   1 oracle   dba           65065 Sep 17 11:04 zot.sql

Now the tricky one:
/home/oracle/Scripts$ dd if=cleanDB.sql of=zot.sql obs=65065 seek=1 127+1 records in.
1+0 records out.

-rwxrwxrwx   1 oracle   dba           65065 Sep 16 12:10 cleanDB.sql*
-rw-r--r--   1 oracle   dba          130130 Sep 17 11:05 zot.sql

See what I mean?
HTH Received on Thu Sep 16 2004 - 20:03:52 CDT