[daip] AIPS user data areas

[Eric Greisen]

computer support writes:

 > I'm surprised, because I thought that at least one disk had to be 
 > required ("+" entry), based on instructions read long ago.  Also, 
 > we found problems if that disk was not writable by any AIPS user 
 > ID ("no disk available" or something like that)...

     In the old days of a few public "big" machines and no private
ones it would help to have a required disk as disk 1, where the users'
SAVE/GET and message files would reside.  Normally now each user has
his or her own machine.  If that user stays only on his/her machine
then things are very much faster and no one steps on anyone else and
disk numbers do not change unless the disk has crashed.  Note that it
takes about 1 second wall time to write one message to the aips
message file over NFS.  1000s of messages may be written in that time
if the disk is local.
 > 
 > Her problem was that, if a disk ahead of hers in our list was 
 > unavailable, the number of her disk (and therefore her catalog 
 > file names or whatever) would change and she wouldn't find.  
 > It seems that making no disks required will make this worse, 
 > as the numbering will now vary even more, depending on what 
 > hosts are given to the "da=" command line option.  
 > 
 > But maybe I'm missing something.  We'll try it that way...
 > Anyway, thanks for your prompt reply on Friday.
 > 

Users rarely invoke the da= option and those disks always follow the
local disks and so do not affect the numbering for the more important
local disks.  When a random collection of machines are all included
then the user will get confused because they have no idea what the
full set of machines is doing.  They should know what 1 or 2 machines
are doing if they choose to include them explicitly via da=.  As I
say, most users here do not even know that that option exists.

Eric Greisen