[j-nsp] M20 - thoughts on dual vs single RE/SSB?

[billp]

We are quoting out some M20's for parts of our network, and were
curious what everyone's school of thought was on running dual
RE's and SSB's.

I don't know if I would want to run without dual RE's, given the
amount of hard drive issues we have had.  I'm not sure what the
MTBF on these is, but the few used RE's we have purchased have
not been the most reliable.  

Anyone have a thought on single vs. dual SSB's?  We have never
had a failure, what have everyone else's experiences been?

thanks
bill