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Date:      Mon, 16 Jun 1997 22:59:42 -0700 (PDT)
From:      Simon Shapiro <Shimon@i-Connect.Net>
To:        Tom Samplonius <tom@sdf.com>
Cc:        FreeBSD-hackers@FreeBSD.ORG, FreeBSD-SCSI@FreeBSD.ORG, "Justin T. Gibbs" <gibbs@plutotech.com>
Subject:   Re: Announcement:  New DPT RAID Controller Driver Available
Message-ID:  <XFMail.970616225942.Shimon@i-Connect.Net>
In-Reply-To: <Pine.BSF.3.95q.970616205623.11254C-100000@misery.sdf.com>

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Hi Tom Samplonius;  On 17-Jun-97 you wrote: 

...

>   Nope, the point was making was that you say the board has a 68030,
> while
> www.dtp.com says it is a 68040.  The 68040 has quite a bit more kick than
> a 68030.  That's a good thing.

This whole thing was atounge in cheek (foot in mouth?) and relates to some 
past employment experience...

...

>   The i960 is not necessarily better.  Especially, not the gutless 20mhz
> version.
> 
>   DPT might be better off with the 68060, as long as the price is right.

Yes, but the logo on the chip is still wrong.  Now take Mylex for example.
Here is a quality, mature product that has the right high tech processor on
board.  Obviously the right choice.

(Hint:  Check out the Unholy union's benchmarks and performance braggings.
 Count how many DPT's are described and hoe many politically correct HBA's
 are listed.  Now repeat once the i960 DPT's are out.)

...

>   How does this work?  Do you need to buy DPT enclosures for this?

You can.  They are actually made by DEC Storage Works division.  There is an
upcoming SCSI standard for all this.  The way it works is simple.  They use
several ``undefined/unused'' signals on the SCSI bus (cable) to transmit
back and forth the necessary data.  the DPT's simply comply with the DEC
de-facto standard.  We are using these enclosues in a HUGE project we are
working on. It is amusing to pull a power supply, fan, disk or even a SCSI 
cable off while doing ls -alR or some nasty RDBMS access and listen to the
siren, watch the red lights flash like mad and still have the disks operate 
as if nothing happened (well, a bit slower on RAID-5).

>   I don't have a DPT enclosure :(, and it doesn't seem that DPT makes
> rack mount enclosures.

Well, guess what? Call DPT, ask for Rene norton and tell her to sell you
the 
same rack-mount she shipped me for evaluation.  It is a rack mount that has
2 power supplies and 6 3.5" slots, or you can take a P/S out and put a 7th
disk in.  If you want, she can send you the proper terminator and
instructions
and then you can split the BUS into 2 busses.  The only objection I hear
here:

a.  The P/S are only available in A/C.  We need -48VDC
b.  Both power and signal cables come off the front.  this is great  for
    service but our marketing people are complaining.

We (Atlas Telecom, my employer) are building an AC-D/C version (using the
DEC
power supplies (3 in N+1), fans, SCSI backplane, etc. in our own box.  It
will
have eight slots, be differential capable and allow bus daisy-chaining.  It
is done is cooperation with DPT and DEC so you should be able to enjoy the
fruits of this effort.

I have evaluated, tested and even participated in the design of more than
one
I/O subsystem in my short life.  The StorageWorks solution is the best I
have
ever seen.  not perfect, Just the BEST.  Same goes for DPT.  I have worked 
with them on several projects for over 15 years.  Never dissapointed, except
for minor things.

...

> > disks are hot pluggable without any software intervention?
> 
>   Again these all sound like features in the hardware module?

The hot-spare capability is a DPT feature.  So it will work regardless of
the
disk cabinetry.  Hot-plugging SCSI (especially single-ended is tricky.
DPt helps out by allowing the use of 528 byte sectors.  Coupled with ECC
memory in the controller, they perform ECC across the SCSI bus.  This cuts 
down (drastically) on the complaints at insert/removal.  If your SCSI bus is
not carefully done, you will still glitch it.  I have tested some very
reputable solutions and wit hthe exception of the StorageWorks, they all
fail.
The test is simple;  

Plug and unplug a drive once per minute and observe
the system console.  If you get tons of aborts (or the DPT beeps like mad
and
will not stop you have a bad disk bay.

What happens is that either the power supply lines glitch and cause several 
drives to spin down (The DPT sees it as a multiple-drive fault and refuses
to play the effected array), or it glitches some of the handshake signals
and
causes the bus to hang.  The way DEC gets over that is with some fancy
circuitry inside the disk module.  the bus is totally passive (albeit
interesting in design).

>   I just use standard hot-swap modules (Dataport VI).  FreeBSD gets
> mighty
> confused when you pull a drive while it is running, but the modules are
> mighty handle for any kind of field replacement.

See above for possible causes.  The DPT HBA handles all the recovery.  You 
simply do not see any of it unless it gave up.  If you WANT to address
devices
directly and eliminate the DPT handling (why?), there is a way to do it.
The initial version of the FreeBSD driver does not support this ``feature''.
> 
>   Are power supplies a big deal these days?  I've never had a good PS2
> supply die, but have had 4 drives die, all in last three years.

Power supplies are funny business.  We were having severe problems with a
250W PS/2 power supply handling insersions/removal of 4 drives in another
disk bay.  The StorageWorks does fine with one 150W P/S handling 8 drives.
Has a lot to do with surge/spike/EMI handling on the OUTPUT side.
Also, one may think that a $400 P/S may have some more design and quality
put into it than a $35 one.

Simon



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