[H-GEN] Tape Drives

Jason Henry Parker jasonp at uq.net.au
Sat Jan 5 23:01:07 EST 2002


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"Frank Brand" <fbrand at uq.net.au> writes:

> #include <prepare_for_jason_tirade.h>

Um, thanks.

> The question of reliability is lessened as, to be a problem, both
> hard drives need to fail together (ie the original hdd and the back
> up hdd).

If you're talking about catastrophe recovery, sure.

> Two drives failing at the one time is possible but not highly
> probable.

You contradict yourself later down when you talk about power failures
destroying all the drives in a machine.

> The
> biggest problem I have with using HDD's in the same machine is when
> the power supply has a massive and catastrophic failure destroying
> both (all) drives...

See?

> this also goes for tape drives...at least you
> still have yesterday's HDD but how quickly can you get a replacement
> tape drive of this type

I mentioned already that having two drives is a good idea.  The last
time I had a tape drive fail I was able to get a new unit couriered to
me the next day.

> But this copies to another hard drive OK you are still using my basic
> concept of using HDD rather than tape

Not rather than.  As well as.

> Of
> course you could have a box with several drives in it and copy to a
> different drive at the end of each day and have daily backups.

Well, I just did exactly that sort of restore, two days after
Christmas, and I can assure you it's no less painful than tape
backups.  I'm happy to see your mileage has varied.

> 5 minutes disk change and
> back in operation as the whole disk has been copied including boot
> files and all...just need to make the boot partition active...of
> course with RAID and mirrored drives you may not need this.

And this is what I'm doing now.  RAID to guard against random disk
failures, tape to guard against maliciousness or catastrophic
failure.

> >One thing I mentioned to Pat last night that bears repeating here is
> >that *in theory* it's a good idea to have two tape units.  If the unit
> >used to write your backups has a head misalignment, and the unit dies,
> >then unless you can find another unit that has the same head
> >misalignment you are essentially up the proverbial creek.
> I made reference to this before regarding lost drives when the power supply
> spews 240 volts all over your box, fusing bearings in anything that moves.

I'm not so sure of the connection, but my basic assertion is that
tapes are *designed* to be removed.  Disks are just as finnicky, and
certainly not any less expensive.  As for 240 volts through the
machine, well, you'd need to have a replacement box, wouldn't you?

Cue waiting a day for it.  Or the expense of having a whole identical
(or nearly identical) box sitting around.  That's money or time that
can be spent on a second tape unit to run verifies, and restores while
backups are being flushed.

In my experience, nature abhors three things:  vacuum, naked
singularities, and unused bandwidth.  If users find out about these
convenient disks lying around, they may be tempted into thinking they
can be used for a bit of extra space on their workstation or
whatever.  Suddenly you have less backup media, and more data to back
up.  Ick.

> I once knew a guy who backed up on floppies...not a big backup but all his
> finacial data.

Okay, fun story time.  My last girlfriend had a laptop; one day I
discovered that she `backed up' her work to a set of floppy disks.  I
was aghast, and spent a good while explaining that her floppies were
*much* more likely to fail than the disk inside the laptop.  MUCH MUCH
MUCH more likely.

I'm sure you all don't need to be told what happened less than two
weeks later.

> >About backups?  You bet.  The whole topic is only slightly less
> >contentious than `which editor should I use?'.
> LOL. Just a bit less contentious as most people use an editor but only some
> people get involved in backing up.

Exactly.

> Backing up is time consuming and costly and unless you do it right,
> why bother. The whole process is a compromise between cost and the
> importance of data to the organisation. Maybe have a tape drive, oh
> no lets get two in case the first one dies, no lets get three in
> case two die on the same day.  Lets make two back up copies at a
> time in case the tape is faulty...eventually the compromise has to
> end.

Like this thread!

Just to clarify here:  I don't disagree (in the usual sense of
disagree) with much of anything you've said, Frank.  I do strongly
believe in using tape to back up data, and using a few disks certainly
helps makes things a bit more convenient.  I've done everything you've
mentioned here, except the removable disk idea.

I think it would be remiss to not recommend tape backups for Pat's
situation, though (a civil engineering firm, IIRC) since he's got a
chance to design everything the way he wants it from the ground up.
There's a reason tape is still the preferred backup media for so many
situations.

jason
-- 
||----|---|------------|--|-------|------|-----------|-#---|-|--|------||
| Men are Figs!                               http://linux.org.au/conf/ |
|                   --Ann Burlingham                   jasonp at uq.net.au |
||--|--------|--------------|----|-------------|------|---------|-----|-|

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