Various Levels of iRODS Server
Level 1:
    . Object Level
    . Paths in virtual name space (/myZone/home/mwan/foo1)
    . Need to query the iCAT for metadata associated with the path
	resource - where and type, physical path e.g., UNIX path on the servers
        time stamps, mode ....
    . A large number of APIs - most in the form rcDataObjYYYYY
        rcDataObjCreate, rcDataObjOpen, rcDataObjRead, rcDataObjGet,
        rcDataObjPut, rcDataObjRsync, .....
    . descriptor L1desc contain state info of opened object.
        L1desc[l1descInx].l3descInx - linkage to Level 3 descriptor

Level 3:
    . Physical File Level
    . Paths are real path (e.g., real UNIX path) 
    . Info such as resource type (UNIX, HPSS), IP address, etc passed down 
        from Level 1
    . A large number of APIs - most in the form rcFileYYYYY
        rcFileCreate, rcFileOpen, rcFileRead, rcFileObjGet,
        rcFilePut, rcFileRename, .....
    . These APIs are called only by Servers to do remote file operations.
    . descriptor FileDesc contain state info of opened files.
        FileDesc[l3descInx].fd - linkage to driver level descriptor 
        e.g. UNIX fd.
    . Remote file operations are done at this level.
    . Fan out to call the driver functions based on file types (UNIX, HPSS...)

Level 4:
    . Driver Level
    . A set of POSIX functions for each driver type (open/read/write/close ...)

Level 2:
    . Not visible
    . Very little or no APIs at this level
    . A lot of misc routines that goes between L1 and L3.
    . e.g., routines that facilitate parallel I/O - eventally call L3 functions
        to do the actual I/O. routines that branch off to handle mounted
        collections, etc.
    . These routines are not in any specific modules or directories. Mixed
        in with L1 modules or in some modules in server/core directories. 


Workflow in the server for same Zone operations:
    . Try to do most of works on the server where the client is connected to
        Query iCAT on the object and resource (remote call if iCAT is remote).
    . Drill down to level L3
        If the file or resource on a remote host, use server-server L3
        API functions.


Workflow in the server for cross Zone operations:
    . For remote zone operations, use server-server L1 API functions
    . Do not go across at L3 
    . Most rules are enforced at L1. Do not tunnel through L3 and bypass 
      L1 rules.