[LDM #QHF-632102]: Running LDM on AIX6.1

Hi Leo,

This is a follow-up to Steve's previous email.

re:
> Two more question please.

> One of the requirements we need to understand is how much
> disk space will be needed to hold Level II data.  From what we have gathered 
> so far, LDM
> will send compressed Level II data at 12 Mbit/sec (25Mbit/sec for severe 
> weather).  The
> data comes through the socket in a compressed state of 10:1.  Once it arrives 
> at the
> target LDM, the data gets uncompressed into a directory structure like the 
> one below at
> Iowa State:
> 
> http://mesonet-nexrad.agron.iastate.edu/level2/raw/

To reinforce the point that Steve made:

- the LDM will send the data as fast as the network between the upstream 
(sending LDM)
  and downstream (receiving LDM) allows

- the LDM instance on a machine provides one or two services:

  - sending/receiving "products" to/from one or more LDMs

  - doing something with "products" that it receives

  LDMs that do nothing with the products they receive other than forward them
  to other LDMs act solely as data relays. Of course, most sites tend to do
  something with the products being received by their LDM(s) :-)

  What one does with products being received by one's LDM is up to the LDM
  administrator of the site.  As far as NEXRAD Level II data, it is typical
  that a downstream site configures its LDM to re-assemble the pieces of Level
  II volume scans back into a single file.  Some sites choose to uncompress
  those pieces and others do not.  The work of reassembling a full
  volume scan in either compressed or uncompressed format is done via
  one or more pattern-action file (e.g., ~ldm/etc/pqact.conf) actions.

  The example you cite at UIowa is what those at UIowa decided to do with the
  data.

re:
> Does the target LDM server decompress the data into the directory structure?

Yes, IF one configures it to do this through one or more pattern-action file
actions.

re:
> would you be able to supply the estimated storage in GB required to store one 
> days'
> worth of Level II data during severe weather?

We don't have that number at our finger tips, sorry.

I can offer two different measures of the volume of NEXRAD Level II data:

- the following URL shows a two day, hour by hour history of NEXRAD
  Level II product volume flowing in the IDD for the most recent two days:

  
http://www.unidata.ucar.edu/cgi-bin/rtstats/iddstats_vol_nc?NEXRAD2+uni20.unidata.ucar.edu

  NB: the data that is flowing is compressed

- the second is the amount of disk space used to store 30 days of Level II data
  for all NEXRAD data flowing in the IDD.  This figure includes NEXRADs 
operating
  in storm, precip and clear-air modes, so the average per station will be lower
  than if it was running in storm mode.  Here are the numbers from a
  machine that we operate:

  1.3 TB

  This represents 148 NEXRADs (some of which are not operational and so
  have very little data) for approx. 30 days.

I hope that this helps...

Cheers,

Tom
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Ticket Details
===================
Ticket ID: QHF-632102
Department: Support LDM
Priority: Normal
Status: Closed