Hi Zhang Biyun:
This is one of those questions that can initially only be answered with "it depends".
If you can provide more information perhaps we can offer more concrete advice.
This sounds like an exercise in capacity planning.
So it depends on factors like:
a) the size of the machines - especially memory
b) how many cpu's
c) disk space
d) are any other programs, processes going to be running
on these machines?
etc, etc.
Also do you have any high availability requirements?
If so you want to spread instances over at least 2 or preferably
more machines for redundancy in the event of failures.
Are all these instances intended to be in the same cluster?
I hope this begins to help you.
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