Small business backups solutions?

Ben Scott dragonhawk at gmail.com
Tue Feb 5 15:24:26 EST 2008


[aggregate reply to multiple people]

On Feb 5, 2008 12:03 PM, Alex Hewitt <hewitt_tech at comcast.net> wrote:
> It's been my experience that these tape drives (and I'm not necessarily
> talking about this specific model) last about 3 years or so.

  It depends on a lot of factors.  The super-cheap drives -- like
QIC/Travan -- are basically a crap shoot.  DLT and even DDS (4mm
"DAT"), if used properly, will likely outlast the computer they're in.
 That means clean them when indicated, retire tapes after rated use
(they don't last forever), and don't use them in an excessively dusty
environment.

> Not only that but you really need to pay attention to the tapes
> malfunctioning because these guys are usually set up with
> minimal user intervention.

  An unsupervised backup system is arguably worse than no backup
system at all.  At least when you have nothing, you're not deluding
yourself into thinking you're protected.  By "supervised", I mean
things like cleaning when indicated, retiring tapes when appropriate,
reading the backup reports to make sure they're functioning properly,
and doing periodic test restores.  I've seen places reguarly changing
tapes on their dead backup drive.  My personal favorite, though, was
the client who purchased a tape drive and tapes, but never took the
tapes out of their shrink-wrap package.

  Most of the above applies equally well to CD, DVD, HDD, or punched
cards, too.  Hard drives don't like high temperatures, and will fail
eventually, just like tape drives.

On Feb 5, 2008 12:16 PM, Kenny Lussier <klussier at gmail.com> wrote:
>>> You can get 1TB drives (SATA) for around $250.
>>
>>   Right, but that's $0.25/GB.  Smaller disks are cheaper, unless your
> > data set is only just over 750 GB and not expected to grow.
>
> Well, the problem with disk to disk in general is that the space is
> finite.

  You misunderstand my point.  Cost-per-gigabyte is lower for the 750
GB drives vs the 1000 GB drives.  If you've got well under 750 GB,
buying more doesn't make sense.  If you've got > 1 GB, you're buying
multiple drives anyway.  Unless you happen to be right around 800 GB
(won't quite fit on 750 GB, but not going to go over 1 GB any time
soon) it's more economical to buy two 750 GB drives vs just one 1 GB
drive.

> You can always add more tapes to a tape set.

  You can always add more disks to a disk set.

  Keep in mind that I'm not suggesting someone buy *just one* external
hard disk.  I'm talking about using hard disk drives as a replacement
for tapes.  So if you would have 12 tapesets in your backup scheme,
you would have 12 disksets instead.  (Where "tapeset" or "diskset" may
mean just one tape/disk.)  If you're carrying tapes off-site (and you
should), you carry the disks instead.

  This is why you have to factor the cost of the external disk
enclosure into the cost accounting.  But those are cheap, too.  It
gets tricky when you start comparing disks and tapes, because one tape
drive can service many media (so the cost of the drive is amortized
over all the tapes), but each hard disk needs its own enclosure.  In
general, tape becomes cheaper the more mediasets you have.

  General public service message:

  Backing up to a single mediaset, while a lot better than nothing, is
still a limited data protection solution.  A single mediaset will only
protect against data loss discovered within your backup interval.
Generally, that's nightly or weekly.  So it will protect against
catastrophic disk failure, "rm -rf /", that kind of thing.  But there
are many other ways to loose data.

  Examples: Accidentally deleting just one extra file and not noticing
right away.  A slowly failing disk, where some sectors are bad but you
don't notice until you go to read them.  A software bug scrambles a
key database table, but you don't notice half the records are garbage
until the end-of-month report.  Disgruntled employee modifying logs to
cover their tracks.  An outside attacker or malicious software
overwrites every disk it can find, including the backup disk.  Fire.
Flood.  Theft.  A single backup mediaset won't protect against these.

  It's fairly simple to implement a multi-tiered rotation.  The most
common scenario: Backup everything in full every night.  Have daily
tapes for Mon, Tue, Wed, and Thr.  Have weekly tapes for Week2, Week3,
Week4, Week5, that get used on Fridays.  Have monthly tapes (Jan, Feb,
..., Dec) that get used on the first Friday of each month.  This gives
you automatic adaptive granularity -- more backups of more recent
changes, fewer of older data.  This tends to fit well with most data
loss scenarios.

-- Ben


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