Read After Write

[Bill Gradwohl]

jludwig wrote:

>I skimmed and greped man cdrecord (man cdrecord | grep verify) and found
>nothing.
>
>You could though do a compare (cmp)
>mounting the ISO on a loop and do a directory cmp.
>  
>
I'm not trying to check an iso. I'm using a DVD as a backup device.

I'm rsyncing whatever I want to backup to a special location 
(/snapshot/boxname/Thu.040812) on a separate physical volume and from 
there I cdrecord that location to the DVD. My version of a disk to disk 
to tape (D2D2T) only substituting a DVD for the tape.

I used diff -r to compare the hard drive location with the DVD, but diff 
complains when it hits a socket file causing the return code to indicate 
a failure when none actually exists. The -r option to diff was 
attractive since I didn't have to use find coupled with zillions of cmp 
executions to compare file by file.

The thought of abandoning diff -r and replacing it with a find/cmp 
combination was distasteful, so I thought about it and figured I was 
wasting my time doing the compares if cdrecord or the O/S did it as a 
read after write process. Trouble is I couldn't find an authoritative 
source telling me that a read after write is being done and I've got to 
have some assurance that the DVD is an exact copy of the staging area.

-- 
Bill Gradwohl
bill at ycc.com
http://www.ycc.com
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