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[LDM #CJZ-347133]: ramdisk question

Hi Karen,

re:
> I have a question about using ramdisk for the ldm queue.  Is it really
> helpful?

Some say yes (Gilbert Sebenste at Northern Illinois University and
Alan Hall at NESDIS/NCDC are two that come to mind immediately), and others
are neutral.  We have used a RAMDISK on one LDM installation that we maintain
here in Unidata, and it worked nicely.  You might want to post an email to
address@hidden to see what the community has to say (NB: you must
be subscribed to any email list we maintain before you can post to that
list).

re:
> Also, if I create a large ramdisk, and put my queue in there, do I need
> to leave an amount of unallocated memory equivalent to my queue in order
> to hold the queue in memory?

I'm not exactly sure of what you are asking...

re:
> For instance, if I have 48G of ram, and make a 40G ram disk (leaving 8G
> free) and make an ldm queue that is 35G I had problems with swap and
> eventually the machine would crash.  So, am I only able to use 1/2 of my
> ram for ramdisk and the ldm queue?

We seem to remember that you are feeding a LOT of downstreams from the
LDM machine(s) that you maintain.  If this is the case with the machine(s) in
question, then it is likely that you are not leaving enough unallocated
memory+swap for all of the processes that are sending data.  Our experience
on our toplevel IDD relay cluster, idd.unidata.ucar.edu, is that the machine
can start thrashing if there is not enough memory+swap to handle all of the
processes servicing downstream connections.

re:
> Just trying to make the best use of my ram give that I just got new
> systems with 128G (haven't even installed them yet!) which are going to
> be devoted to ldm -- and the huge amounts of data we are moving around
> internally.

I think that we chatted with you about your setup when you were here for
an LDM workshop, and I have a vague recollection of mentioning that it
is important to leave enough memory for OS and LDM-related activities.
I also seem to recall that we pointed out that we do not use RAMDISKs
on idd.unidata.ucar.edu, and the various nodes in that cluster seem to
work well.

Cheers,

Tom
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Ticket Details
===================
Ticket ID: CJZ-347133
Department: Support LDM
Priority: Normal
Status: Closed