[H-GEN] Linux Backup

David Jericho david.jericho at bytecomm.com.au
Fri May 9 21:27:19 EDT 2003


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On Fri, May 09, 2003 at 10:05:21AM -0400, Robert Brockway wrote:
> Hi David.  Demonstrably, harddrives & CD fails far less often than tape.

Hard drives, yes, I'll agree. CDs. No.

CDs can suffer the same problems as tape in many ways. I've burnt CDs
on various different drives over the years, that can only be reliably
read on that very CD burner. Caveat emptor and all the rest. Same goes
for DVD.

> DDS tapes don't reliably store data past a year & can only be written a
> very limited number of times.  Harddrives typically last 5 years or more
> and can be written hundreds or thousands of times.

As opposed to CD media which simply does not have the capacity for
large amounts of media without spending a large sum (i.e. the cost of
a SDLT drive) on an autoloader for a burner?

I'm a very firm believer in the concept of "you get what you pay for"
when it comes to backup.

> > Not that I'm defending tape, but the problem appears to be there is no
> > better solution.
> 
> I think there _weren't_ any better solutions.  The firewire drive I use
> is robust.  A small business could get two of these and rotate so one was
> always offsite. 

What I dislike about the use of disk for backup is that people do get
lazy, and don't hotswap/unplug the unit simply because it can be
difficult. How many PCs do you still see with firewire ports only on
the rear?

Leaving a drive connected to the machine it's responsible for just as
silly as storing your tape collection in the hot cupboard by the
stairwell.

> One of the worst things about tape is head misalignment - when a tape may
> be perfectly good but only the original tape drive will restore it.  Too
> bad if the original tape drive dies in the same disaster that killed the
> computer and made you invoke your disaster recovery.

I've always made a point of confirming on a regular basis that my
backups can be read back on another machine with a similar drive. I consider 
the likely hood of two different model tape drives misaligning in the same 
manner is very slim.

I've also always confirmed that if I use dump under Linux, that I can
restore it under Solaris, and vice versa. The most interesting and
particular attributes may not be restored, but what is most important
to me is the data, not the system particular attributes it may have.
Same goes for tar and the rest.

> I don't mean to say that tape solutions aren't _ever_ useful, but I
> think that in many situations there are now viable (imho superior)
> alternatives.

I don't see anything wrong with disk as backup, but I see disk as
fragile as a tape itself. Drop a disk, and like dropping a tape, you
may as well replace it. You can never be sure.

Disk makes an excellent short to medium term store of backup data, for
quick restore and the like, but I don't believe in it for anything
longer. Unless it's wiped each use, block checked, and then verified
after, you can't be sure you haven't suffered critcal hardware failure 
that'll cause loss of data.

I'm not sure that I believe in the use of a filesystem on a backup device 
anyway[1]. It adds an extra point of failure. I'd much rather just treat the 
entire device, be it CD, disk or tape as a raw device and layer my files 
in a simple archive format on top of that.

In anycase, nothing practical yet beats paper for long term storage.

[1] Was it not 2.4.14 that was out for a matter of hours before it
    wiped a few peoples filesystems?

-- 
David Jericho


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