I am preparing to replace 6 smaller dataservers with 2 much larger 
systems and I am curious if anyone has advice on making the transition. 
  There is about 40TB of data currently on the smaller dataservers.

A couple of caveats:
1) The existing data is organized in cache groups on the dataservers and 
the cgroup information will need to propagate to the new dataservers

2) The smaller dataservers are in a production system and I want to 
minimize any downtime associated with data on these servers.

3) A sizable portion of the 40TB is no longer relevant to the production 
system and potentially could be deleted (or at least not migrated)

It eases my burden if I can delete data from all the production 
dataservers at the same time.  However, if I delete data from the 6 
servers that will be migrated, I don't want new data to take its place.

I was hoping that I could somehow setup the existing dataservers in a 
readonly configuration but still be able to delete data via the 
redirector (actually from a FUSE client talking to a CNS service on the 
redirector).  Is this possible?

 From my reading, I can make the dataservers readonly by altering the 
all.export line:

all.export /xrd readonly

But I am not sure if this still allows deletions.

Also, does the use of oss.cache directives affect the readonly status?

If anyone has experience with performing this type of migration, or if 
anyone has suggestions, I would be very thankful to hear from you.