Re: Backup media in stray fields

Steve Philson (philson@nmr.chem.umn.edu)
Mon, 12 Jun 1995 12:18:31 -0500 (CDT)

fry@chem.wisc.edu writes:
>
> I have been informed that our Journal of Chemical Education: Software
> group has obtained floor space on the floor directly under our Unity
> 500. They plan to place a software development group in the rooms
> below the 500, with some duties involving making up distribution
> floppy disks (Mac and PC) for mailings, and performing network backups.
> (We have 12 ft ceilings.)
>
> I immediately responded that they couldn't possibly find a worse
> location in Chemistry to locate these people; apparently they had
> to work hard to obtain any new space at all, and under the 500 was
> a spot that wasn't highly desired by others (wonder why :).
> So JCE wants to proceed if possible: they have requested I
> obtain more precise information.
>
> I would appreciate any comments about how high a field you believe
> such operations can safely be performed. The identities of any
> respondies will be not used!!! so please feel free to give your
> best estimates or describe if you perform backups, for example,
> in 10 gauss fields. All I can do at this point is forward a best
> estimate from a group like this and from vendors (I'm hoping
> some fairly accurate estimates will come from MRI community, but
> would still appreciate emperical data from this group).
>

I have no authoritative information, but I have had experience with
running computers and backup devices near magnets. Our Mac IIfx is
well within 10G line of our 300 MHz wide bore, and the computer itself
and hard disk have given no problems. We have had a rewritable
optical drive fail, but its replacement has proved much more durable,
and I don't attribute the failure to the field. The floppy does seem
to have problems, and presently is not working at all, but who knows
why floppy drives fail. Some of our Sun boxes are in >10G field, and
the only failure we have seen was in a DAT tape drive (WangDAT) that
kept eating tapes. It continued to do so long after it was moved away
from the field, so I cannot be certain the field had any effect, but
we have kept our new one (an HP, with a different tape handling
mechanism) farther away from the magnets and it has given no problems.

The general consensus seems to be that you need to keep the general
population outside the 5 G line, and that warnings must be posted and
traffic limited inside it. In your situation the people directly
below will probably be working close to the 5G line, and you may have
to have someone make measurements if the room is to be general access.
They will certainly see distortions in their computer monitors, and
may need to be made aware of field effects. I usually don't worry
about having a floppy disk or a magnetic tape in a 5G field, but you
have to be careful of other things. Steel tools and other objects
become magnetized. The local fields from these objects may be much
greater than the steady stray field that magnetized them, so you can
create a whole army of harmless-looking things that can damage data if
floppy disks or tapes are set next to them. I have never seen
warnings about this, and would be happy to learn that my fears are
groundless, if someone has better information. That is why I am
posting this back to the ammrl too.

-- 
Steve Philson           philson@nmr.chem.umn.edu
Director NMR Lab        612-626-0297
Chemistry Dept.         University of Minnesota