[Mimedefang] Question about limiting size of TMPFS volume

Michael Sims michaels at crye-leike.com
Tue May 20 10:36:01 EDT 2003


Hi,

Sorry if this is in the archives; I couldn't find it.

I've been using TMPFS for my MD spool directory for the past week or so and
it's been working really well.  My machine has 1 GB of RAM and I have
allocated 500 MB for the TMPFS volume using the "size=500M" option to the
mount command.  I have configured Sendmail to accept at most messages that
are 20 MB in size.  So, in order to ensure that my spool volume doesn't fill
up, I have limited the number of MD processes to 22, so that I fall under
the limit with a nice bit of wiggle room.

It seemed to me before that I needed to plan for the worst case scenario (22
concurrent SMTP connections, each transferring a message that is 20 MB in
size), but after watching the server for a week I'm noticing that the TMPFS
volume seems to hover around 1% utilization most of the time.  And this
makes sense, even though I will accept a single email that is 20MB in size,
the vast majority of email messages are 3-10k.  And my understanding of
TMPFS is that it doesn't reserve any RAM until it's needed, and swaps unused
pages out to disk, just like memory allocated to programs.

So, I'm thinking that I can safely increase the number of children processes
without adding more RAM, and not have to worry too much about filling up my
TMPFS volume.  But, if I do there is an outside possibility that this will
happen.

Which leads me to my question (sorry to take so long to get to it), which is
this:  What will happen when MD attempts to create a new spool directory and
isn't able to write to the volume?  Will this cause it to send back a
temporary failure to sendmail?  Because this is actually what I would want
to happen.  I could increase the MX_MAXIMUM and not have to worry, because
if the spool was temporarily too large the server would tempfail and the
remote host would try again later.

Thanks in advance...

___________________________________________
Michael Sims
Project Analyst - Information Technology
Crye-Leike Realtors
Office: (901)758-5648  Pager: (901)769-3722
___________________________________________




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