[Simh] RT-11 Storage Strategy

[Henry Bent]

On 16 February 2016 at 23:33, Will Senn <will.senn at gmail.com> wrote:

> All,
>
> The array of simulated disks available to simh is a little confusing to
> wade through. I tend to use RL02 and RK05, but really, I don't have a solid
> rationale for one over the other. In RT-11 these are available when
> attached, so their what I use. I'm hoping someone can offer some more
> informed storage advice/strategy.
>
> Here are some questions to get the juices flowing:
>
> In SimH with a PDP-11 running RT-11:
>
> * Is there a preferred disk controller/device?
> * Is there a controller that supports more disk devices than another (RL
> vs RK, etc)?
> * Does one device have more capacity than another (either via single disk
> raw capacity or via overall capacity of attached units)?
> * Is one device/controller more reliable in SimH than another?
> * Do disks need to be formatted before initializing?
> * Are there some known best practice configurations (so many RL
> controller, with so many drives, or so many RL and so many RK, etc.)?
>
> Here's where I'm coming from as background. I have been studying Macro-11
> programming in RT-11. I save all of my files on a storage disk that is
> separate from the SY: volume (DK:, etc.). I have found working Pascal,
> BASIC, and FORTRAN distributions that can be installed. Rather than
> installing them into SY:, It seems reasonable to attach a disk, assign the
> disk a logical name, and copy each distribution onto its own vol, something
> along the lines of SY:, PAS:, BAS:, FOR:, and MAC:, with 5 disks attached.
> But, before I headed down this road, I thought I would get some advice.
>
> Thanks for reading and thanks in advance for responding with your sage
> advice :).
>
> Regards,
>
> Will
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Hi Will,

I know that this isn't quite what you were asking, but on my real 11/23
running RT-11 I have four RL02s (well, a Dilog DQ614 and an MFM disk
emulating four RL02s) and that is more than enough storage for my
purposes.  In addition, if you know that you aren't going to need all of a
physical disk for a specific purpose, you can just mount a disk image as a
logical disk.  For example, I have CDISK.DSK and TCPIP.DSK on DL2:, and
those images are mounted as C: and TCP:.

SIMH allows for four RL02s at 10MB each and eight RK05s at 5MB each, so
there's no difference in total storage.  As far as I'm concerned it's
somewhat more convenient to have a smaller number of larger capacity
disks.  If you need a full 80MB of storage I don't see why you couldn't use
both controllers/disks.  You could also use RD5[1-4] disks (DUx: to RT-11,
the RQ controller in SIMH) if you really need more space, though I believe
RT-11 is limited to 32MB on a single filesystem so you would have to
partition the larger disks.

My understanding is that there is not a "preferred" disk controller or type
under SIMH.  I have found that for an emulated Ultrix system, running off
of an RD54 is noticeably faster than running off of RL02s, but on a
reasonably fast host system you probably won't notice the difference under
RT-11.

My final note is: if you're curious about something, just try it!  Make a
backup of your current working system and then go wild.  That's the fun of
SIMH.  Want to see if RT-11 will recognize an RA82?  Or sixteen RC25s?
Does RT-11 work with a TU56 DECtape?  I have no idea what the answer to any
of those questions is, but I know how to find out.

-Henry
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