[Info-vax] OT: the Daily WTF for today is a VAX/VMS story

[Kerry Main]

> -----Original Message-----
> From: Info-vax [mailto:info-vax-bounces at info-vax.com] On Behalf Of
> Johnny Billquist via Info-vax
> Sent: 14-Feb-16 6:50 PM
> To: info-vax at info-vax.com
> Cc: Johnny Billquist <bqt at softjar.se>
> Subject: Re: [New Info-vax] OT: the Daily WTF for today is a VAX/VMS
> story
> 
> On 2016-02-15 00:05, William Pechter wrote:
> > In article <cld7pc-g5j1.ln1 at news.chingola.ch>,
> > Paul Sture  <nospam at sture.ch> wrote:
> >> On 2016-02-14, JF Mezei <jfmezei.spamnot at vaxination.ca> wrote:
> >>> On 2016-02-14 04:48, already5chosen at yahoo.com wrote:
> >>>
> >>>> More I think about it, more the story of VAX hard drive with
> >>>> three-phase AC motor (in early 90s, non-the-less) appears
> apocryphal.
> >>>
> >>>
> >>> RA82 drive motors were 1/3 horsepower motors. They were not 3
> phase, but
> >>> required 3 wires in. There was one used to start the motor in the
> right
> >>> direction as I recall.  There was some capacitor that would discharge
> to
> >>> get motor going. I don't recall the exact details.
> >>
> >> I know nothing about the wiring details, but two or more RM05 drives
> could
> >> be connected together so that they spun up in sequence to minimise
> the
> >> maximum current draw.
> >>
> >> And yes, I had a customer who reported that as a hardware error :-(
> >>
> >> --
> >> There are two hard things in computer science: cache invalidation,
> >> naming, and off-by-one errors.
> >
> > Yup and the RP06's could even share a power socket with a cable DEC
> shipped
> > that let a pair of drives daisy-chain the AC power between them.
> >
> > And a power sequence cable kept them from trying to power up at the
> same time
> > IIRC...
> 
> You know, I've never seen a power sequence cable for the RP06, but
> when
> I was reading the documentation now, the manual mentions the power
> sequence control. So obviously there must have been a way to connect
> them together for that purpose.
> 
> Our DEC-2060 had three RP06, but I cannot remember any power
> sequencing
> going on between them. But maybe 3 was considered too few. Or,
> actually,
> I think we also had them all on separate fuses...
> 
> 	Johnny
> 

There was a small 2 or 3 pin signal cable which was strung between 
drive power controllers to enable power-up sequencing. 

It was highly recommended best practice, but not mandatory. This was 
not unique to RP's, but was actually used by RMxx/RAxx and numerous 
other drives at the time. I believe you could setup systems powering on
the same way.

Reason was that these drives had very high startup current and after a
computer room power failure or just normal power off /on maint work,
if this sequencing was not in place, then the Data Center UPS/PDS's 
breakers might not be able to deal with the current from all the drives 
restarting at once.

Regards,

Kerry Main
Kerry dot main at starkgaming dot com