[Soekris] SMTP on Soekris?

Chuck Yerkes chuck+soekris at 2003.snew.com
Tue Feb 4 06:41:06 UTC 2003


Quoting Michael Sierchio (kudzu at tenebras.com):
> Chuck Yerkes wrote:
> >Your CF will be written to a lot.  It will become less than useful. ...
> 
> This is not immediately clear.  Writing to CF is slow, but each "region"
> should sustain 10M writes.

We keep hearing numbers, but don't see evidence for *anything*.
I know Sam Leffler was looking for information, but I haven't see
anything.  Has anyone taken 100-200 CF disks and hammered them with
data until they failed?  It's not sensible for hobbyists, but one
might expect it from any of the vendors who are shipping CF booting
devices in bulk.

>  If you mount a FS rw,noatime,sync it's
> probably fine.  If you implement a stable queue yourself you can
> guarantee that the writes are distributed evenly over the CF.Q
> 
> SMTP semantics are such that an OK after a DATA must guarantee that
> the bits and their metadata have been committed to magnetism (or
> whatever) -- this is seldom actually the case, what with Softupdates,
> async, HW write caching, etc.

Mail semantics from someone who has worked with mail a *lot*.

After the OK, the data "must be committed to permanent storage".
When ReiserFS and Ext3 fs, the sendmail folks looked very closely
and made a couple changes to the code to ensure that the directories
are sync'd as well (AFAIK).

Softupdates (via Kirk McKusick) when used with Sendmail (led by
Eric Allman) follow the RFCs devoutly.  Kirk knows plenty about
sendmail and Eric knows plenty about file systems.  The messages
are safe and crash proof (barring media corruption).

re: async writes, sendmail documents that you *must* have the mqueue
directories on non-async partions.

HW write caching depends.  There have been scary disks that say
they have written, but they haven't written.  That's really bad.
With real RAID systems, any caching *must* be non-volatile.



If you need a mail/AV system, the soekris is not the right box.
64MB RAM with no swap and ~133MHz 486 is lovely for lots of things,
not mail with A/V.  I love the box for several thing. The 45x1's
are not mail machines .

Oh yeah, if mail cannot be delivered, the qf file (for sendmail)
gets rewritten on each delivery attempt to update information.

10M writes isn't so many, really.  2 files/message.  10 million
writes with perfect delivery doesn't handle 20k messages/day (fairly
small business) for very long (250 days).

While I can put a screw in with a hammer or a pair of vice grips,
using the right tool for a job is a better approach.



More information about the Soekris-tech mailing list