I am really curious with all these SAN technologies and that all of it calls
for quiescing the disks i.e. stopping writes for a brief sec(s) to take a
snapshot..

How does one write applications or consider uptime in a situation as such ?
Even a slight blip and application tend to fall on their face . How does one
work around this on a very busy OLTP system ? Any suggestions ?

Thanks

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I would suggest you read up on "DBCC FREEZE_IO" and associated commands, and
contact your SAN storage vendor to see if they have any layered products to
assist you in this. Many storage vendors will have packages which on one
hand integrate with SQL server (VDI interface) and on the other hand
integrate to the storage to automate these type of executions.

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?

Applications should be written as normal, how you consider uptime is up to
you, if you freeze IO (to disk) for 5 seconds, but don't disconnect your
clients.... is that up or down ? you need to answer that question for
yourself.

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Go back to the Application developers, even when for some reason the
application gets disconnected, it should have mechanisms build in to
reconnect at lease configurable say retry 3 times and time out of x
seconds.... if an application "fall on their face" upon a disconnect... then
the application will fail upon a cluster-move-group... it really should try
to reconnect... with all respect, but this is bad client app programming