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testing - 1998 - January - this message

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From: mark@[REDACTED] (Mark Salyzyn)
Date: Tue, 6 Jan 1998 11:03:45 -0500

gdb@dbsystems.COM (G. David Butler) writes:
> Mark Salyzyn  writes:
> >The DPT controller is the only one that supports RAID, with the added bonus
> >of up to 64MB of Cache.
> RAID is ok, I guess, but Cache that isn't battery backed up or
> doesn't follow the OS's sense of "write this data now, really"
> is a BAD thing.

There is a philisophical problem with battery backup Cache, that is for sure.
DPT (internally) has a Battery Backed up PM3334 card, but none of our OEMs
want it ...

Sync (command 35 in the SCSI command set) flushes cache on both the card and
the drives. This is the command that is issued by our other drivers to ensure
clean shutdowns, critical data paths and just before a SCSI bus reset.

As for the Battery Backup issue, one will need to ensure that there is
continuous power to the drives as well since their sense of Cache also
gets lost during power outages and SCSI Bus resets. The consensus is that
since the drives have their own problems with Cache, that a UPS is a far
better investment than YABRS (Yet Another Battery Replacement Schedule) for
the server market we generally target our controllers for.

The Battery backup card, if ever released, will be in the higher end PCI
or I2O product lines.

Disclaimer: This is my opinion and does not reflect DPT's opinion.

>>All the above DPT PCI cards do circles around the 154X series of cards. In
>>fact, our lowest end ISA based controllers (I know, John's driver doesn't
>>support them, but it can since there is no difference to the interface
>>ports and command sets if you force the I/O addresses) are 40% faster than the
>>2940s and none of our cards are as slow as the 154X's as well!
> I'm interested. Is the PM2041W a ISA/DMA busmaster?

Yes, suffering from the same ills as all ISA cards, the 16MB limit. John did
not set up any bounce buffer technology in his driver, once that is done if
the system has more than 16MB of memory, forcing the address, to lets say 01F0,
will work.

Your mileage will vary, as my comparison was a direct result of the BSDi
BSD/OS 2.1 driver.

> How many can I put in one machine (i.e. which DMA channels and IRQ's
> does is support)? What is the DMA transfer speed?

DPT ISA cards can be placed at 01F0, 0170, 0230 and 0330. However, they only
have three possible interrupts (12, 14 and 15) limiting you to three ISA
cards in a system (some motherboards allow for ISA interrupt sharing through
a wired-or gating of the interrupt lines).

> I will try to get a technical reference manual on the PM2041W,
> and if successfull, I will give the controller a try.

Shhhh, you may wish to indicate that you intend to evaluate the card and
be modifying a driver to run with this card and that your evaluation will be
posted on the worldwide plan 9 discussion list ...

Sincerely -- Mark Salyzyn