Re: NT vs AS/400

Neil,

You're right when you say that the drive consists of more than an enclosure.
Specifically, a hard drive consists of the following within the enclosure:

-disk platters
-spindle shaft & motor
-read/write heads & armatures
-actuator
-preamp circuitry
-air filter & pressure vent

These are the most costly components of the drive, and are identical across
the various interfaces (IDE, SCSI etc).

Attached to the outside of the enclosure of all modern drives is a printed
circuit board (PCB) that provides the electronics necessary for physical
control of the motors. The PCB also hosts the physical interface,
configuration switches, and a controller chip.

The controller chip on drives destined for the AS/400 production line are
likely modified, but my guess is that this is limited to embedding some kind
of an ID that is recognized by the SLIC, in order to lock us into using only
those drives sold for the AS/400. The fact that you can get an AS/400 drive
working in a PC with a SCSI subsystem supports my conclusion.

Moving right along, let's address the often touted advantages of those
special AS/400 drives. Specifically, I'll address the ones you mentioned:

1) Predictive failure analysis

This is not exclusive to the AS/400, nor has it ever been. Please consult
the following references:

http://www.storage.ibm.com/oem/tech/pfa.htm
http://www.storage.ibm.com/hardsoft/diskdrdl/ultra/ul73lzx.htm

The advantage for the AS/400 is that the SLIC and OS/400 directly react to
the drive feedback. On xSeries machines running NT/W2K/Linux, there are
separate software applications to handle this. The software is usually model
& OS dependent. In the case of my Netfinity/NT boxes, this package is called
the Netfinity Service Manager.

2) Better reliability

Hard disk reliability is measure by MTBF, and is most often determined by
the quality of components and operating environment. It's the stuff inside
the enclosure that usually fail, not the PCB. Reliability problems caused by
microcode generally show up early, cause consistent problems, and are
addressed by installing a fix.

I've installed microcode fixes for the SCSI drives on our Netfinity, and for
the IDE drives in our workstation. There is nothing magical about this that
is exclusive to an AS/400. Of course, IBM written microcode is not going to
work on a BCC drive, and BCC can't upgrade the drive controller through
OS/400 & SLIC, so that's a definite problem with 3rd-party drives on AS/400.

3) AS/400 IOP's

How a hard drive comminicates with a processor is referred to as "Transfer
Protocal". There are two types of transfer protocals; PIO Mode (Programmed
I/O), and DMA (Direct Memory Access). SCSI drives use PIO mode to talk to a
processor. The operative word here is *a* processor. They neither know, nor
care that the processor in question happens to be an IOP instead of the main
CPU.


After the last few days of participating in this thread, I'm probably
beginning to sound like a mischiefmaker who's only interest is stirring the
pot. That's not entirely true. I *am* trying to stir the pot, but my goal is
simply to challenge the erroneous claims that are routinely made to defend
the business practices of IBM. This strategy of blind loyalty to the brand
and summary dismissal of anything not born in Rochester, is akin to sticking
one's head in the sand to evade a predator. More importantly, when it
includes the use of half-truths and otherwise misleading information in the
message, it only serves to discredit the messenger, and his campaign.


John Taylor
Canada

p.s. Neil, this was a general rant, and in no way directed at your
personally.



----- Original Message -----
From: "Neil Palmer" <neilp@dpslink.com>
To: <MIDRANGE-L@midrange.com>
Sent: Saturday, June 02, 2001 09:51
Subject: Re: NT vs AS/400


> Not that it justifies the entire price difference, but you are not
> comparing apples with apples here.  There's more to the disk unit than the
> base disk enclosure.  Rochester adds the controller & microcode to those
> drives (what gives it better reliability, predictive failure analysis
> capabilities, and ability to work with the IO processors).  There is
> obviously some overhead costs associated with that work that are added to
> the price of the disk unit.  (And when you buy 3rd party disk like BCC you
> don't get those controllers or microcode, which is why some disk related
> PTF's won't work with non-IBM disk, and in fact could cause problems).
>
> ...Neil
>


+---
| This is the Midrange System Mailing List!
| To submit a new message, send your mail to MIDRANGE-L@midrange.com.
| To subscribe to this list send email to MIDRANGE-L-SUB@midrange.com.
| To unsubscribe from this list send email to MIDRANGE-L-UNSUB@midrange.com.
| Questions should be directed to the list owner/operator: david@midrange.com
+---