[conspire] Burn DVDs...

Rick Moen rick at linuxmafia.com
Wed Jan 8 16:00:48 PST 2003

Quoting Jose Sanchez (jose_sanchez79 at yahoo.com):

> It is very true what you have posted. I get "maybe it will work" from
> almost everyone I talked too. I need this solution to backup important
> data not movies and stability is what I am after. I might just have to
> put a tape drive instead :)  

Yeah.  Doing backup to DVD _sounds_ attractive and nicely high-tech, but
I'm not sure you'd like the results:

1.  Capacity is OK (4.7 GB).  About right for home machines, I guess.
2.  Cost-effective media?  I haven't priced the blanks, but suspect
    they're pretty damned expensive per MB, compared to, say, DDS3 tape.
3.  Backup speed?  Is each backup going to take a dog's age?  I'm not 
4.  Verification.  A backup is worse than useless if you can't trust its
    integrity.  (If you make unreliable backups, you're suffering a 
    false sense of security.  If you know that you have no backup, you're
    at least scared and cautious.)  Standard backup mechanisms have 
    verify cycles and/or extra tape heads that do hardware-level 
    read-and-compare, to ensure that you actually have useful data.
5.  Cataloguing and media rotation/reuse.  Regular backup mechanisms
    keep records of what data are on which backup sets, so you can
    determine which set has the last version of your master's thesis 
    before you accidentally deleted it.  And they also tell you how 
    much wear each backup set has gone through, and therefore which
    ones to recycle next and when to retire sets from service. 
    (Of course, if you're using write-once media, this isn't an issue.)
6.  Software support for incremental and differential backups, not 
    just "grab everything" backup jobs.  Easy to do with tape; can
    you do it with DVD?

All of the above issues come up all the time on Linux mailing lists,
whenever someone proposes goofy ideas like "Hey, lets do backup onto
CDRWs!" just on account of being gadget freaks and not thinking through
the details.  And you'll hear a lot of _really_ bad advice in most such

There's also a difference between backup and archival storage.  Are you
sure you're trying to do the former and not the latter?  I'll not get
into the difference right at the moment, but it has to do with what
you're trying to protect against.

Maybe you'll feel like expanding a bit on what you're trying to
accomplish, if you'd like to get better-aimed advice.

I have a partial summary of common tape-backup types, here (omitting
some crucial details such as pricing):

Some rather acidly worded mail from me to Karsten Self regarding the
gadget-freak problem in backup discussions is preserved here:
(Also includes explanations of differential vs. incremental and backup
vs. archival storage.)

'Hope that helps!

Cheers,                                      "My file system's got no nodes!"
Rick Moen                                    "How does it shell?"
rick at linuxmafia.com  

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