[HECnet] RT-11 filesystems, was Re: DECnet-RT?

[Steve Davidson]

Dave,

RT11's file system can only address 32MB of space.  It only uses a
clustersize of "1" so it is limited.  Partitioning the disk into
logical areas was the way the DU driver got around this.

You are correct that the RM drives are limited to the first physical
32MB of disk space.  They did not use partitioning until the DU class
of drives came out.  The reasoning was that the older drives would not
be around much longer anyway so why bother.

I wrote a driver (handler in RT11 speak) for the RP06 that eventually
made use of the partitioning scheme that the DU devices used.  I got
the idea from Greg Adams (the original author of the DU driver/handler)
but alas, it is long long gone!  Oh well...

-Steve

On Tue, 2020-03-31 at 14:10 -0400, Dave McGuire wrote:
> On 3/31/20 10:02 AM, Robert Armstrong wrote:
> > RT11 has an architectural limit of 32Mb per file system.  Most disk
> > drives, even way back then, are bigger than that and have to be
> > partitioned if you want to use all the space.  This is an RT11
> > thing,
> > not a CDROM nor a PDP-11 nor a simh, feature.
> 
>   So, about that.  And please forgive the non-HECnet-related
> question.
> 
>   Like everyone here, I've run RT-11 since the dawn of time.  But
> I've
> never run it on a disk that's larger than 32MB that is also not MSCP.
> 
>   On a (real) system at the museum the other day, I noticed that RT-
> 11
> has a driver for the RM02/RM03, a 67MB drive.  I went looking as I'm
> bringing up a Fuji M2284K SMD drive, which (on an Emulex SC21 Unibus
> controller) emulates two RM02s.  If RT-11 cannot partition an RM02
> because it's not MSCP, then why does it have a driver for it?  Will
> it
> just use the first 32MB?
> 
>   Or (similarly to Ethernet) was it just there to use "raw"?  I know
> of
> one installation (on an 11/70) that used RM02s for raw storage of
> digitized audio, no filesystem.
> 
>               -Dave
>