Date: Thu, 5 Mar 1998 20:38:37 +0100 (MET) From: Wilko Bulte <wilko@yedi.iaf.nl> To: dmlb@ragnet.demon.co.uk (Duncan Barclay) Cc: shimon@simon-shapiro.org, julian@whistle.com, scsi@FreeBSD.ORG Subject: Re: SCSI Bus redundancy... Message-ID: <199803051938.UAA02731@yedi.iaf.nl> In-Reply-To: <XFMail.980305080650.dmlb@computer.my.domain> from Duncan Barclay at "Mar 5, 98 08:06:50 am"
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As Duncan Barclay wrote... > > On 04-Mar-98 Simon Shapiro wrote: > > > > On 04-Mar-98 Wilko Bulte wrote: > > > > ... > > > >> An extra power supply is money well spent. We ship all our standalone > >> arrays at least with N+1, optional 2N power. 2N gives you 2 seperate > >> power entry points to the power grid. Now we only need to educate people > >> to use two different power branches (phases? what's the right English > >> term?) > > > > The old DPT 9W tower (made by DEC) had an interesting feature, where the > > power INPUT was switchable too. If the AC to one supply went dowm it will > > draw AC from the other. > > > > Yes, 2N P/S is trivial to do (2 diods/circuit if I remember right) and > > cheap. Technically, you want each supply fed from a different phase. In > > the US they are referredto as ``independant circuits''. I have seen people > > paying lots of money to get that, where they have 220V right in the same > > room (220BAC in the US is 2-phases, 180 degrees apart, unlike the European > > 3 phasees 120 degrees apart. Yest, you can get 3phase circuits in the US > > too). The hot wire in a 220VAC, in the us is 117VAC to ground, 220VAC > > hot-hot. > > > > Are you sure you guys want to use different phases of a the same feed? Remember > all two or three phases come into the building from the same sub-station down > the same pice of cable. Most comman fault is a digger cutting this > cable taking out all three phases or temp. shorts in the Yep, we had an example of that at work ;-) > overheads to the sub-station (auto reset ater a couple of minutes; usually > from wind blowing the cables together). We are lucky: our low voltage net (anything <220kV I think) is almost all underground lines. At least no arcing lines. More digger risk of course ;-) > > You need feeds from seperate sub-stations. You are of course right. But in my personal experience asking for what you propose really drives customers up the wall. In most cases people don't even know how their power grid is put together. Having things like this changed proves to be horrendously expensive. But again: if they really care they should shell out the Dfl ($). But in general I think the Dutch power grid is not really comparable to the US: for the best part underground, much shorter distances etc. Interesting side step: the same thing applies to long distance fibres for remote disaster tolerant sites. PTT tends to route these things very nicely through the same trench (but you can at least *see* them do that most of the time, and hopefully correct 'm...) but also thru the same phone/network switch(es). Cute.. Wilko [ moved to -scsi ] _ ______________________________________________________________________ | / o / / _ Bulte email: wilko @ yedi.iaf.nl http://www.tcja.nl/~wilko |/|/ / / /( (_) Arnhem, The Netherlands - Do, or do not. There is no 'try' --------------- Support your local daemons: run [Free,Net,Open]BSD Unix -- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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