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20030804: ldm back data (cont.)



>From: address@hidden
>Organization: ULM
>Keywords: 200308041746.h74HkZLd017877 LDM request

Adam,

>So, the larger the queue the older the data that you can request??
>(example.  1Gig = 1 hour  4Gig = 4 hours??)

No.  The larger the queue _on the upstream host_, the older the data
you can request from that host.  Your queue size does not determine the
age of the oldest data that you can request.

>If that is the case, how big of a queue can you make??

>The machine that i want
>to extend how far back it can feed out is a SPARC IIe Sun Blade 100 running
>Solaris 8(last revision before 9 came out) all patched up.

Again, you are dependent on your upstream site's LDM queue size.

>I remember reading
>somewhere that 8 and below version can only have a 2 gig queue but if you were
>running 9 on a 64 bit machine that you can have files larger the 2 gig.
>Is this right or can you build larger queues with a 64bit and Solaris 8?

One can build the LDM with large file support on Solaris SPARC 8,9.  For
instance, we are running the LDM on the top level IDD relay node
thelma.ucar.edu with a 6 GB queue.

One can also build the LDM with large file support under Linux and
FreeBSD as long as the queue size is less than approx. 4 GB on those
OSes.

You have to remember that the LDM queue is a memory mapped file.  This
means that you should not make queues larger than your physical RAM
or you will get into heavy disk swapping by the OS.

>Just tring to get things straight.

The key thing to remember is that the IDD is a store and forward system.
The only data that can be forwarded to a client (a downstream site) is
the data that is available on the server (the upstream site).  We try
to get IDD relay nodes to run with as large a queue as they can.  How
large is dependent on how much RAM they have and what kind of machine
they are running.  Essentially all of the very top level IDD relay
nodes are running with 2 GB queues.  Thelma.ucar.edu and atm.geo.nsf.gov
(both Solaris 9 SPARC machines) are running with queues larger than
2 GB: thelma's queue is 6 GB; atm's is 4 GB.

>Thanks

No worries.

Tom