[conspire] Backup

Nick Moffitt nick at zork.net
Sun Feb 4 03:29:03 PST 2007

Roger Chrisman:
> Is it risky to run your backup drive in the same server it backs up?
> How risky, technically? (Lets pretend these are SCSI drives and
> without RAID.)

Yes, it's pretty risky.  But a backup volume on a separate spindle
within the same machine is still Way Better Than Nothing.

In my experience, the two things most likely to fail your data are
drives and user error.  The drive situation is why we have RAID, but
that occasionally has the "bulbs all burn out at once because we
installed them at the same time" problem.  There's an argument that a
dedicated backup spindle will have a different pattern of wear-and-tear
than a system drive, and is less likely to have a simultaneous failure
with your system volume.

User error is the other big one.  Gotta love how "crontab -e" is so
easily mistyped as "crontab -r" on a QWERTY keyboard.

Both of these are handled pretty well by the situation you describe.  In
the event of a power failure or system board malfunction, the drives
could be migrated to a temporary host system and brought up either as a
complete resurrection or as a temporary fileserver for the backed-up

In the event of a fire (meaning your box gets doused by the sprinklers)
or other complete system fry-up, you can count on starting from square

My instincts say that this sort of backup is a bit of a 90% solution.
It's good enough that it stops people from going the other 10%, and you
often do need to weigh the costs of going to a proper offsite backup on
archival media such as magnetic tape.  

The old arguments about incremental or versioned backups on removable
media are somewhat moot, as you should first be storing /etc and any
other important regularly-touched trees in bzr or mercurial or similar,
and rdiff-backup has the very handy "reverse incremental" system that
you just plain can't do with tapes.

Also, tapes are just not keeping pace with the speed and volume of
modern multi-terabyte arrays.  It's rather disappointing.

"If, as they say, God spanked the town                          Nick Moffitt
for being over frisky,                                    nick at teh.entar.net
why did He burn the churches down
and save Hotaling's whisky?" -- 1906 SF Earthquake rhyme

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