[H-GEN] Assistance Required

David Jericho david.jericho at bytecomm.com.au
Tue Mar 26 21:32:10 EST 2002


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On Wed, Mar 27, 2002 at 09:58:35AM +1000, Robert Brockway wrote:
> > Or burn CDs. For a business, that can be nicer; creates a nice archive
> > that lasts for a while.
> 
> Hi Arjen.  My problem with CDs as backups is recovery time.  How much time
> does it take to restore 30Gb off 660Mb CDs?  How messy is it?  How much
> fun it is while the entire company is sitting around waiting for you to
> finish because someone trounced the fileserver?  Fun fun fun :)

About the same time as tape, if not slightly quicker, assuming you've
done your backups right.

I would have waited till Saturday, but jetskiiing maybe an option
given the weather, so I'll put my two bits in now.

As I see it, there are a few problems with backups.

1) Longevity and durability (social, and physical) of backup media.
2) Speed of restoration.
3) Ease of restoration.
4) Dependance on particular software/hardware.

The longevity and durability of media is a real downside of CD media.
How many times have you noticed an office worker spotting a CD without a
recognised label (i.e. without the MS hologram) just lob it straight
into the bin on a cleanup? I've seen it too many times, and CDs always
go walkabout regardless of how well you keep track of them.

CD platters also seem to degrade over time, chunks go missing from the
insides, and CD blanks which don't do this cost a fair bit. No $0.30
CDs for backups. And it's not one small sequential block, but lots of
small sequential blocks. 

Tape on the other hand has a slight advantage on the social side,
people not recoginising them will often come ask. And a lot is known
about the longevity of tape media, having been in use for as long as
digital computers have been around. So long as you don't keep hitting
the same peice of tape over and over, and the tape is kept in a
healthy environment, it can keep backups solid for 10 years or more,
assuming your tape drive isn't sick.

Then again, if your backup media goes wandering, I'd address the issue
of where it's kept, and why people have access to it.

Tape, CD, they all restore at roughly the same speed, unless you've
got some uber l33t0 DLT tape unit (in which case, you already know all
of this). Then it comes down to how long it actually takes you to get
at the data stored on the media.

A SAGE-AU magazine a few months back had a short article discussing
backup solutions and software, and time taken to actually rebuild the
machine back to the point where the data on the media is useful. In a 
previous life, I had a beta level system where I could whack in a
CD, rip the old partition information off the backup server and fdisk
the machine up, and then just start a command to zap that data across
the network to the newly created partitions. Took 5 minutes plus the
time to actually transfer the data to restore a machine in its
entirety. Of course it took a few minutes more and some hardware
shuffling if the backup server had imploded.

Ease of restoration comes down partly to how well you've documented
your procedures, and what dependancies you have. If you were as the
sys admin to be (God forbid) be hit by a bus on the way to work, could
the receptionist restore a system that blew up the night before? Or
did it take someone a tad more competent like a fellow HUMBUGer or a
consultant to do so? Would they waste half a day merely figuring out
how your potentially obfuscated and convuluted system worked? Will
they need to use only one backup, or a series of backups to get the
system to a current state?

Was there a document written in plain english, with step by step
commands, on how to do both single file restores, and whole system
restores?

Did the entire backup depend on some scripts written by some author
who shared their code via freshmeat, that resided on the now defunct
system? Did anybody know, or could potentially find out where to
obtain these scripts? Does the actual media depend on a particular
peice of hardware? Do you know of anyone who has the same equipment
that you maybe able to pull in a favour from?

There are dozens more questions that can be asked, but I look at
backups from the perspective of worst case scenarios. 

As an example, the office burnt down overnight and the system admin
got hit by a bus on the way to restore some important data that was
needed for continuation of business from another location. 

Solved by offsite backup storage, with a reliable company, with
detailed instructions contained with the media on how to restore the data, 
in what format it is in, and if who maybe able to help in the
situation they have no ability to do the task themselves.

Backup servers are an entirely different conversation.

--
David Jericho
    Ma ta-uh dolla. Nah tree fiddy, own-la ta-uh dolla. 

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