Re: Have DVD burner, will backup!

["David E. Fox" <dfox@tsoft.net>]

On Tue, 20 Jun 2006 21:38:05 -0600
Nate Duehr <nate@natetech.com> wrote:

> Requirement: Single touch, full-backup?  Faster speeds in case 
> interation is required?

Well, that would be nice. :)

In the "old" days when my biggest disk was 1.6 gig, I got a DAT tape
drive precisely for easy backup - and at the time, 4mm DAT media were
the cheapest way to go (other tape methods were far more expensive),
although the hardware itself was a bit pricey.

Back then, I could do a full backup just by doing 'tar cf /dev/st0 /' -
and the whole disk content fit on just one tape. Now my HD storage has
grown. Of course, the more data you have to backup, the harder it seems
to actually do the backup.

Now that a single DVD+RW media costs about maybe 25 cents US and holds
twice as much data as 4mm DAT, I think that DVD+RW is a better
solution than tape is. But obviously you just can't tar to the dvd like
you could do to tape (maybe with packet & dvd-ram, you can).

Of course, tar has this nasty downside that if the file you need to
restore is at the end of the tape, you get to wait until the end of the
tape to retrieve it. With a dvd, you just mount it somewhere, pull the
data off, and go.

> Requirement: Restores take less/no space from the existing system.

Let's take a look at this point for a bit. Sure, if I needed on tape to
restore a given file, all I would have to do is to tar the file from
the tape. As long as I don't use any compression (and/or if the backup
media stores data just like a file system copy), I can mount the disk
with the data I need, and if it's not on the first set, it could be on
the second or third (or fourth, etc.) and either it will require me to
remember what's on what disk, or have a cycle of mount, peek at
contents, umount, insert next disk, mount, peek at contents, etc. That
may be a whole lot quicker to accomplish than having to retrieve
the whole archive set from the media prior to a restore,as dar seems
want you to do. 

Still, backing up a (nearly) 30G HD to three DVD-RW wasn't all that
bad. But I'd still have to keep the archive on HD (the .dar files
themselves), or copy each dvd over in turn, then run a dar restore or
incremental. Here, it seems that if I'm going to reuse the space taken
up by dar archives for other things (due to a lack of space to begin
with) I just might as well do full backups each time.


> Requirement: Back up everything - /home only is sub-optimal.

Different parts of the filesystem change at different rates. It's
always a good idea to do a full backup - that way you at least have a
full backup in case something goes wrong. But if you're running stable,
much of the system isn't going to change - but of course, /home will,
and likely other parts as well (/var). When I was working with tape,
I'd frequently back up /home, maybe other partitions as well, but of
course /home was a whole lot smaller back then as well.


> It seems to me (and MANY sysadmins have already "gone here") that with 
> the current cost of hard disk space well below the price of removable 

I have no disagreement with that - only that the incremental cost of a
new disk is greater than a bunch of removable media disks :).  

> on the device, hopefully), 

> 
an external disk may just flat out be 
> "better" when viewed from a requirement-fulfillment point of view.

I agree - and going that route, all the backup "software" I would need
could just be 'rcync'.

> 2. External hard disks are slightly less portable than DVD's.
> 
> 3. External hard disks *might* take up slightly more phhysical space 
> over DVD's, depending on the size/density of the disk.

And you can't really just plug them in (hotswap) as easily either.
They're more of a permanently "there" setup. OTOH, several years ago I
visited a local shop where they had these external "cage" things where
you could just plug an HD in from the outside, and not have to open the
case. Of course, you can simply connect a USB or firewire drive without
having to open the case, and likely without having to power down the
system to change drives.

But that was circa 1997, and it got me thinking. Back then a very
popular setup were "zip" drives and they were very restrictive storage
wise (by todays standards) and the media cost a fortune. I figured that
as long as HD prices continued to plummet, and allowing for an easier
way to swap HD drives around (i.e, these front-mountable cages, for
one) that "zip" technology was doomed.

> 4. On REALLY big backup jobs, finding a single external disk to cover it 
> might be difficult, but at those sizes, DVD isn't really a very 

I'm not yet in that league. But it goes back to an early point - the
more data you have, the harder it is to back up. 


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