Read After Write

[Cameron Simpson]

On 11:25 12 Aug 2004, Bill Gradwohl <bill at ycc.com> wrote:
| jludwig wrote:
| >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. [...]
| 
| I used diff -r to compare the hard drive location with the DVD, but diff 
| complains when it hits a socket 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.

The OS certainly doesn't. And by default cdrecord doesn't.

Why not just "rsync -n" back from the DVD to your data and see if
anything's been missed?

Cheers,
-- 
Cameron Simpson <cs at zip.com.au> DoD#743
http://www.cskk.ezoshosting.com/cs/

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