Subject: Re: Backup Software Question
From: Harald Wagener (hwagener@fcb-wilkens.com)
Date: Wed Aug 01 2001 - 04:52:51 EDT
Chris Garrigues wrote:
>
> > From: Harald Wagener <hwagener@fcb-wilkens.com>
> > Date: Tue, 31 Jul 2001 10:47:02 +0200
> >
> > Chris Garrigues wrote:
> > >
> > > > From: Christian Schmidt <ChriSchmiLi@gmx.de>
> > > > Date: Mon, 30 Jul 2001 22:52:13 +0200
> >
> > [snip]
> > > > Well, a backup stored on a HD isn't a real backup IMHO, is it?
> > > > What if your backup-HD crashes?
> > > (by the way, I fon't think I wrote this, but the argument still holds true).
> > > what if your tape becomes unreadable?
> >
> > well, too bad, I hope You check Your backups regularly for consitstence and
> > functionality.
>
> I do. This is easy to do on the RAID array where they live.
>
> > > How is a backup on a hard disk not a backup?
> >
> > It's not a _real_ backup. It's a redundant storage with identical points of
> > failure. Since hard discs are random access media, they can also be randomly
> > deleted. This is harder with tapes that are handled properly, i.e. stored in a
> > fire proof water sealed safe off site.
>
> It's also harder to do when it's on an off-site RAID array to which the users
> only have read access. I wouldn't consider it as having identical points of
> failure since it's on a different hard drive using RAID technology instead of
> single drive technology on a different computer system on a different (but
> also secured) network in a different building on a different power grid.
If You take systems safety as I learned it (I might be wrong, anyway), the
differences between a
hard disk and a RAID array can easily be seen if You draw a fault tree: the points
of failure are the same,
but in the RAID array failure of one disk is 'not critical'.
most important here is that there is a different network and a different power
grid.
Just to be nitpicking: The power grid is also served by another power
company/power plant?
I assume You have an UPS at hand, so this would weaken the criticality of this
point as well.
But this is entirely different than the scenario someone offered, where You have a
machine in hot standby that simply gets a copy of the original machine's hard disk
each night.
> > Secured tapes, even if they are stored in the same room as the machine being
> > backed up, are also less affected by power surges or other electrical
> > instabilities (as long as the sparks don't fly...).
> >
> > It is also easier to replace the read/write mechanism (i.e., the drive) when using
> > a tape backup solution than it is with a hard disk.
>
> Easier than replacing one hot-pluggable drive in a RAID array?
a hot pluggable drive in a RAID array is not the typical hard disk on a hot stand
by machine
(i.e. not everybody can afford a RAID system, even a second one just for the
prupose of backup systems).
>
> > So, if You take care of Your backups, there is a significant decrease in Your
> > chances of losing data. Nothing of this is foolproof, nonetheless.
>
> This is certainly true, but it doesn't have anything to do with whether the
> media is tape or disk.
By the way, it does. It depends on the MTBF of the media used. In Germany for
example, You need to store
financial data that has been digitally produced for ten years for the tax
collectors to check if You did everything right.
print copies won't suffice from 2002 on. How many disks You use are older than 8
years? 12 years?
Long term storage of magnetic tapes is a field well researched. Not even CDs come
close, if You remember the press about certain
fungi destroying cd's (in extreme weather conditions, they say today). It's also
true that it is often difficult to get tape readers that read tapes used ten years
ago (Your university might have one, but it probably won't work anymore).
Well, I think we can agree that if the storage used is significantly different
(the difference vector
containing factors such as physical distance), the chances that Your backup
solution will help You
in disaster recovery will rise as significantly.
> I just like not having to change tapes every day.
That's the reason why automated libraries exist.
> I also like my users being
> able to restore their files through a web interface that I wrote.
And we would like our users not to delete their files in the first place (-: .
This cannot be technically prevented on the working set
As has been said before, different solutions serve different needs of different
people.
I am quite confident that Your solution works sweet for You. And I don't see my
point
being attacked by Yours. Your solution is an alternative to mine and covers the
most important
points needed to have a backup rather than a copy. If You want to discuss this
topic further,
I suggest we do it off list since we are pretty much off topic right now.
Regards,
Harald
> Chris
>
> --
> Chris Garrigues http://www.DeepEddy.Com/~cwg/
> virCIO http://www.virCIO.Com
> 4314 Avenue C
> Austin, TX 78751-3709 +1 512 374 0500
>
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> explanation of what we're doing, see http://www.DeepEddy.Com/tms.html
>
> Nobody ever got fired for buying Microsoft,
> but they could get fired for relying on Microsoft.
>
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-- Harald Wagener | Systemadministrator FCB/Wilkens GmbH | Tel.:+49-40-2881-1252 An der Alster 42 | Fax.:+49-40-2881-1263 20099 Hamburg | http://www.fcb-wilkens.com
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