Hi all,
Just to follow up on Ron's comment, which he and I discussed on the
way out of the TechAssess telecon this afternoon...
On Jul 31, 2006, at 4:07 PM, Ronald Lambert wrote:
My feeling is that current disk MTBF is much less than that figure,
and would propose writing a minimum of two sets on the summit to
maintain data integrity. If we have to drive disks down the
mountain in case of fibre failure we don't want that to be the only
copy.
ron
I think a good argument can be made for two copies of the data on the
mountain, based on at least two points...
- we discussed a "policy" that there should ALWAYS be two copies of
the data on spinning disk. To implement this as soon as possible,
one needs two copies of the data on the mountain. This is
particularly true if the mountain-base link is down, and the base
copy doesn't get written.
- this is the case Ron mentioned: if the mountain-base link is down
for more than (say) 24hrs (not gonna happen except in really bad
circumstances), then our fallback position is to unplug a set of
disks (probably 1 4U unit) and truck it down the mountain. One
CERTAINLY does not want to throw our ONLY copy of last night's data
in the back of a truck that will be traveling down a dusty, curvy
road. One wants a second copy to stay safe and sound on the mountain
until the traveling copy gets written into the base architecture and
transferred to the archive center.
I'd imagine that this is not a significant cost factor... only a few
TBs. :-)
Cheers,
Chris
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Dr. R. Chris Smith EMAIL: [EMAIL PROTECTED]
National Optical Astronomy Observatory
Cerro Tololo Inter-American Observatory
950 N. Cherry Ave. Casilla 603
Tucson, AZ 85719 La Serena, CHILE
Office: 520-318-8555 FAX: 520-318-8170
WWW: http://www.ctio.noao.edu/~chris
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