[svlug] archive media of choice for 10~100GB

[Rafael Skodlar]

On Thu, Jan 01, 2004 at 01:24:58AM -0000, John Conover wrote:
> Mark S. Bilk writes:
> > 
> > Disks (and tapes) can be wiped by a magnetic field.

Of course, it's RW media.

> >
> 
> It would be a really, really, big EMF-the strength of the rare-earth
> magnets used in the head servos of hard disks is measured in Oersteds,
> (yes, Oersteads,) and don't degrade the platter data.

Disk drives have metal casing which prevents most of the magnetic field
from the outside to do any harm to data. Additionaly, most computers
have metal case which adds to magnetic field protection. Laptop drives
are more sensitive of course.

> 
> The Library of Congress went through this several years ago to start
> archiving data electronically, and after a long scientific study
> decided on R CDROMs. The gold-bond CDs are good for about a hundred
> years, (extrapolated MTBF data, of course.) But there is an issue with
> long-term stability of CDs when read-they are blasted with a class 2
> visible light laser device, which will degrade the data if read enough
> times.
> 
> If the data is not accessed on a regular basis, either a HD or CDROM
> would be adequate. The dominant failure mechanism in HD is seek
> errors, (the mechanics of the head servos wear out, meaning a head
> crash,) so the MTBF is roughly proportional to cumulated seeks, (if

That's where poor software comes to play, ...

> the HD is unplugged and stored off line, it will last as long as the
> grease in the bearings-about a quarter of a century.) If CDROMs are
> not read, the MTBF is proportional to the stability of the
> medium-about a century.
> 
> In both cases, the device's electrical interface would be obsolete
> before the data crashed, (for example, try and buy a 5.25 floppy to
> recover data stored a decade ago,) the data could not be read even
> though it was intact.

Not hard to find that. I've seen that advertized somewhere on the net
...

I still have that kind of drive around. Used it about a year ago to move
old data from floppies to Linux box.

> 
> As with stuff electronic, keep things cool and dry-the MTBF gets cut
> in half for every 10C increase in temperature.
> 
>         John
> 
> BTW, streaming tape is kind of out of the question for what the poster
> wanted. Going through the MTBF data, it is about 18-24 months, if used
> only once, (which is OK for daily backup, but not for archiving.)
> 
> BTW, the best MTBF I have found is the Fujitsu SCSIs. They are small,

Agree, Fujitsu is one of the best HDD manufacturers since many years
ago.

> (about 20G, max,) pricy, and not that fast; but they list 1.2 million
> hours, (assuming ergodicity, according to their QA Dept.,) as an MTBF,
> (which is over a century,) operational. 8 disks-a hundred+ GB-would
> have an MTBF of about 17 years, and the data would be recoverable for
> certain types of failures, (but not, for example, if the power supply
> nails the +12V to the 30V unregulated, and smokes everything-which is
> the next most common electrical/electronic failure in PCs after the
> HD.)

Don't agree here. Most data on burned out disk drive is still there and
recoverable. If you are lucky, and the motor in HDD is still good, it's
not too hard to recover it. If the motor is bad, then the only option is
to take the drive to one of specialized places to reassemble it to a
working unit and recover the data.

I managed to do just that without paying hundreds of $ to a data
recovery company after both, primary (ATA) and backup (SCSI) drives
burned out in a PC with bad power supply. Fortunately, the drive motor
was still good to solve the problem. Motherboard, CPU, and memory smoked
literaly. Fuse in bad power supply is still good ;-)

> 
> -- 
> 
> John Conover, conover at rahul.net, http://www.rahul.net/conover/

-- 
Rafael