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Date:      Thu, 3 Oct 1996 13:25:23 -0500 (CDT)
From:      Joe Greco <jgreco@brasil.moneng.mei.com>
To:        richard@pegasus.com (Richard Foulk)
Cc:        jgreco@brasil.moneng.mei.com, jeff@mercury.jorsm.com, freebsd-isp@FreeBSD.ORG
Subject:   Re: RAID Controller Product
Message-ID:  <199610031825.NAA07158@brasil.moneng.mei.com>
In-Reply-To: <199610031815.IAA13726@pegasus.com> from "Richard Foulk" at Oct 3, 96 08:14:46 am

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> } The other non-obvious downside to this is that the reason you are
> } doing it in the first place is so that newsreaders can connect.  However
> } once connected they like to stay connected for a long time... and when
> } you bring the other machine back online, you are going to have a SECOND
> } service disruption.
> 
> Hadn't thought of that.  In that light, more reliable servers (with
> RAID, etc.) may be more appropriate than multiple/redundant servers
> (since that's where this thread started.)

Is it, though?

If you take a machine from 98% to 99% reliability by introducing RAID,
etc., you have just halved your downtime.  That is good.  However, you
still have 1% to worry about.  If you have completely redundant servers,
as long as they do not all go down simultaneously, you have 0% to worry
about BUT you may have some minor transitional hiccups due to cached
DNS entries, etc.

Therefore...

The way I look at it:

More reliable single machine = good chance for occasional total failures

Multiple machines = small chance for total failures, but there may be
	a few bumps along the way through the transition due to caching
	DNS, crappy clients, etc.

So, it would seem to me that the latter is preferable particularly if you
minimize the "bumps" by reducing TTL, etc.  I would rather be able to tell
a customer that they simply need to try to connect again than have to tell
them the news server is dead and the ETA is 18 hours because an expensive
RAID SCSI controller failed.

... JG



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