19 Jun
2009
19 Jun
'09
9:27 a.m.
Pete Turnbull <pete at dunnington.plus.com> wrote:
The note that I read didn't say anything about power requirements, as
far as I can remember. But maybe I should check the note I read again.
This was about six years ago... (And as far as I know, the site is still
running that machine, but they now have a couple of SCSI disks on it
instead.)
It could be that there are two revisions of the backplane? (Was it you
who said that?)
I know for a fact that a steel plant in Sweden stood still for five days
because of this, six years ago. (Well, one part of it anyway.)
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt at softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
On 17/06/2009 16:34, Johnny Billquist wrote:
Ok. I haven't checked all the details here, so it's part my research,
and part information I've recevied from others. The only reason I even
know about it is because I had to recover the data from a disk that they
"destroyed" by doing this.
> It's actually worse. The write enable
signal apparently always gets to
> both drives no matter what else you are doing. So when you write to one
> drive, the other will also start writing, even if the head is moving
> right at that time. I've had to recover an RD53 which was destroyed that
> way. (Salvage as much data as I could, and then reformat the drive.)
That won't happen unless both drives are also selected. Having the
write enable signal go to both drives at the same time is normal in
ST412 systems, and indeed all the signals go to all the drives at the
same time in such systems. > The funny
thing is that DEC actually do write in the documentation that
> it is not permissible to have two hard drives in a BA23, but that note
> is not so easy to find, and if you don't have the documentation, it even
> easier to assume that you can, since you do have connectors for two drives.
The DEC information actually says that it's because of the power
requirements. > I believe
it's a hardware "bug", which can't be fixed without cutting
> wires, and adding new ones. But maybe someone knows better here?
Mine works, and I've not cut any wires.