Skip site navigation (1)Skip section navigation (2)
Date:      Mon, 12 Oct 1998 10:12:01 -0400 (EDT)
From:      Bill Vermillion <bill@bilver.magicnet.net>
To:        freebsd-fs@FreeBSD.ORG
Subject:   Re: filesystem safety and SCSI disk write caching
Message-ID:  <199810121412.KAA15041@bilver.magicnet.net>
In-Reply-To: <199810121326.GAA09753@salsa.gv.tsc.tdk.com> from Don Lewis at "Oct 12, 98 06:26:05 am"

next in thread | previous in thread | raw e-mail | index | archive | help
Don Lewis recently said:

> Even with an UPS, a large percentage of our unclean shutdowns are
> power related. Most of these are due to power outages that last
> longer than our UPS batteries. I don't think there is enough room
> in our building to store enough UPS batteries to last through our
> typical winter power outages. I don't think we'll be getting a
> backup generator anytime soon, and even then I've heard quite a
> few stories on freebsd-isp about problems getting generators to
> reliably start.

Today's UPSes typically have self-monitoring capabilities to put a
signal on a pin when they reach a certain minimum capacity.  At
this point they will send a system shutdown command.

If you have nothing as sophisticated as that, build your own.

Have a normally open 110VAC relay.  Connect two contacts
to the TX/RX pins on an RS232.  Push something through that ever
minute or so.  When the signal can't be passed the system will not
get this signal - indicating the power has failed on the relay and
it opened up (barring some other failure).  If your battery is good
for 20 minutes, use a routine like this.

If no signal (eg no AC to relay), start timer.
Set a variable to 10
Every minute check the connection.
If not connected decrement the variable.
If power comes up, stop countdown routine.
If power still not there software monitor the relay
will issue a shutdown when the counter decrements to zero.

As to getting generators to reliably start - good systems from
known vendors usually work well.  It's the home-brew units that
lack niceties.  At a radio station I worked with a zillion years
ago we had a motor-generator set that we were required to have
(one of the EBS stations), and that had to be run once per week,
also another legal requirment.   

It was a Ford V8 running on propane.  Always started - no problems
- but it was homebrew.  At the end of the require hour on the air
with it running all the clocks would be about 5 minutes slow and
all the records play about 5-10% underspeed.

Current offerings from companies such as Best - will use Onan or
Sony for their small systems.  Software automatically tests them
once per week by starting them an running them.  Options are large
tanks to extend running time with no refills to days, etc.

Good equipment almost never fails.  Cheap equipment quite often
fails - and Murphy's law dictates that it will fail when you most
need it.


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-fs" in the body of the message



Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199810121412.KAA15041>