On Feb 20, 2006, at 9:11 PM, Bruce Black wrote:
I am, most concerned with the "copy that is perhaps miles (up to
1000's). Where I last worked (IIRC) we had approximately 160
volumes that were XRC'd that went from Chicago to Colorado then
back to NY. The (only other) copy being in Poughkeepsie. This is
old information so it might have changed from then.
To me, the information that was bounced around the US was so out
of date it seemed like a waste of effort to do so. I know that XRC
and "dual copy" which (to me) is what you are talking about are
similar. I think the main issue is "distance, IIANM.
Lets look at it this way: the data sent remotely by PPRC or XRC
might be a few seconds (worse case a few minutes) out of date.
But if your datacenter becomes non-operational (there was another
message in this thread about a data center being bombed!!) then at
least you have your data, current to a minute or so of your live
data. If you have to depend on offsite backups, the data will
probably be a few days out of date. If the currency is so
important, and the company is willing to pay the freight, remote
mirroring is a good practice.
My earlier messages were talking about local mirroring, because the
thread started talking about tape vs disk speed and related to
backup times. Local mirroring allows backups to be "created" in
very little time, and then moved to tape outside the backup window,
so the tape speed becomes less important.
Bruce,
It does indeed come back to what's in the controller and what is in
the pipeline. As you said it could be seconds or X seconds. That is
why the pipeline needs a large bandwidth. I personally would not call
it instant by any reasonable stretch though.
But who am I to challenge the experts?
If they (probably you) want to call it instant, fine.
Ed
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