Skip,
As I wrote the distance and the treffic type decides whether ESCON is
applicable or not. In your case - 100km, remote CU - it's not.
BTW: It seems the earthquake is limiting factor for you, why don't you
get rid of the earthquakes? We don't use earthquakes at all...
<vbg>
BTW2: I live on watershed. We don't have rivers, lakes, floods, mines,
earthquakes, tornados, airports in the neighborhood, even terrorists.
The most dangerous natural threats are pickpockets and burglars. <vbg>
Seriously: A datacenter location should be planned carefully and the
most important factor is natural and "human" (like airport) threat
existence.
Regards
--
Radoslaw Skorupka
Lodz, Poland
W dniu 2011-06-23 22:58, Skip Robinson pisze:
Radoslaw,
I'm sure that your experience was perfectly valid for your geography. I've
heard that it's fairly common in Europe to rely on a recovery site that
lies only a few KM from the primary site. 'Across the river and through
the woods.' (Woods optional) In the U.S., recovery distances are almost
always much greater. Along the West Coast, for example, the biggest threat
to an IT environment is earthquake. You have to reach pretty far to find a
site that won't go down in the same seismic event.
At distances of 100 KM, ESCON over DWDM is a dog because it's a
synchronous protocol: each STARTIO has to get a positive response before
the next operation can proceed. With every KM, the round trip time
increases. As you mentioned, conventional channel extenders (CCE here)
mitigate the delay by spoofing both the computer on one end and the device
on the other end. CCE allows ESCON to pump data faster than it could if it
actually had to wait for a real response to every operation.
FICON is designed to ship a boatload of data in one burst before requiring
a response, which can be returned even as data is going the other
direction. Hence DWDM fiber can be (more) fully utilized. Data flies.
This anecdote illustrates the performance improvement we saw. All of our
tape drives at both centers are accessible to all systems at both sites.
'Local' or 'remote' tape is selected by esoteric name. For many years we
ran ESCON tape with CCE. Users were accustomed to a remote tape taking
longer to process than a local tape. Shortly after we converted remote
tape from CCE to FICON/DWDM, we received a 'problem call' from a user who
was certain that his job had somehow allocated a local tape drive instead
of the intended remote tape. Elapsed time was too short for the job to
have run correctly!
Incidentally, our original motivation for moving from CCE to DWDM was
cost. The performance boost was icing on the (cheaper) cake.
.
.
JO.Skip Robinson
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