MSCP SCSI CD-R(W)?

Jerome H. Fine jhfinedp3k at compsys.to
Sat Mar 4 09:06:11 CST 2006


 >Tim Shoppa wrote:

>There was a special-order option for at least some CMD controllers
>that allowed you "raw" access to the SCSI device, all packaged
>up and delivered through special MSCP packets. I saw this used
>in the 80's with laser-disc type storage but have not seen it
>since.
>
>Emulex sold UC07's/UC08's with special firmware for talking to
>some optical-write-once SCSI things too, but I think it hid it
>all behind some normal-ish (not "raw SCSI over MSCP") MSCP stuff.
>
>At this point it's probably easier to just put a NCR 5380 on the
>Q-bus or something. Heck, that was probably easier 20 years ago :-).
>
Jerome Fine replies:

About 15 years ago, I attempted to produce a WORM
device driver under RT-11 called WO(X).SYS for
an optical WORM drive.

It split the device between the RT-11 directory
at the start and the remainder of the device.

I seem to remember that I used the Dialog SQ706A
in the normal manner for the WORM device which
had a separate off-drive controller for the drive
and MFM / ESDI set of cables for the actual drive.

It actually worked quite well and I still have the
media I had to purchase for the test - since once
it was altered it could obviously not be used again.

All I am saying is that there did not seem to be
anything special about the WORM drive / media
except for the WRITE  ONCE restriction.  Otherwise,
the SCSI interface acted in the normal manner and
once all of the files had been written to the WORM
media, the RT-11 file directory was also placed there.

At that point, the media was set to be READ  ONLY to
be protected against accidental WRITEs and used in
the normal manner as a standard SCSI drive with the
standard DEC DU(X).SYS device driver.

Just my experience with hardware that never seemed
to catch on very well since READ / WRITE optical
drives such as the Sony SMO S-501 appeared within
a year or two and made the WORM technology obsolete.

As for the original subject which started this thread,
I use a CD-R all the time for backup, although it is
actually a DVD-R since the backup image file is about
800 MBytes and just a bit too large for a CD-R.  Every
4 months, I save the last backup image file of the month
to the DVD-R which creates a permanent record with only
3 * DVD-R per year.

In addition, if the DVD-R drives / media were not available,
I would definitely have used a CD-R for a permanent backup.
I have a number of 600 MByte ESDI hard disk drives on the
PDP-11 backed up on Sony SMO S-501 drives / media and
then transferred to DVD-R media.  Since I have about 5 of
these 600 MByte files and all fit nicely on just 1 DVD-R
with room for a few other files, it was much easier to
have the single DVD-R for everything.  In general, I regard
a DVD-R as just a higher capacity CD-R.

Finally, because a CD was actually required and since there
is only about 131 MBytes of files, I did produce a CD of
RT-11 distributions which is actually able to boot RT-11
directly from the CD-R if the hardware supports 512 byte
blocks.  As Zane has mentioned, that is possible with some
CDROM drives / SCSI host adapters for the PDP-11.  In
addition, the PC that I use with a Pioneer A05 DVD drive
also supports 512 byte blocks with full access to the first
16 CD sectors or 64 equivalent hard disk block which is
where the RT-11 directory resides for the first RT-11
partition on the CD of 32 MBytes.  I have booted RT-11
as a test on the CD a number of times under E11 although
it is just as simple to MOUNT the ISO file for the CD
that is on the hard drives - and much faster.  Note that
before I had the Pioneer A05 DVD, when I attempted to use
an IDE CDROM drive, I could not boot RT-11 since the
driver prevented E11 from reading the first 64 blocks with
the RT-11 directory.  Fortunately, I was still able to
complete my test of the CD by using a SCSI CDROM drive
on the PC and asked E11 to MOUNT the SCSI drive instead.

So a CD-R is an excellent media for permanent storage.
Just how long it will last is another question.  I plan
to read my CD-R and DVD-R media every year and test them.

In that regard, does anyone else have a regular testing
period for their files permanently saved on CD-R or DVD-R
and how many years seems to be reasonable?

Sincerely yours,

Jerome Fine
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