Is it possible to run multiple MapReduce against the same HDFS?

[Zhenhua (Gerald) Guo]

I plan to deploy a HDFS cluster which will be shared by multiple
MapReduce clusters.
I wonder whether this is possible.  Will it incur any conflicts among
MapReduce (e.g. different MapReduce clusters try to use the same temp
directory in HDFS)?
If it is possible, how should the security parameters be set up (e.g.
user identity, file permission)?

Thanks,

Gerald