Changing the number of file headers on an RSX volume

Kenneth Gober kgober at
Wed Jun 24 11:57:44 CDT 2020

On Tue, Jun 23, 2020 at 9:03 PM Chris Zach via cctalk <cctalk at>

> So I'm working on this RSX11M+ system here and while working I ran
> myself out of file headers. Using the HOME /MXF command I was able to
> increase the number of headers, but only up to 4090. or so. Trying to go
> to 4100 gave me an error saying there were not enough system blocks or
> something. Currently I have 830 headers, but that's not enough in the
> long term.

I've never actually used RSX-11 myself, all I know about it is what I read
in the ODS-1 spec, but I'm guessing the issue here is that the volume is
set up with only 1 block allocated for the index file bitmap, and growing
the number of file headers beyond 4096 would require growing the index
file bitmap to 2 blocks (or more, depending on how many file headers you
expect to need).  Since the first 16 file headers must follow directly after
the index file bitmap, growing the bitmap requires moving those first 16
file headers as well, which in turn requires moving whatever may currently
be in the way.  None of this of course is something I'd expect the system
to be able to do while the volume is mounted.

What precisely you have to do to achieve the goal of having a volume
with more file headers I can't say, sorry, but I thought I could at least
provide some extra context for other readers on why it's not as trivial to
do as one might guess.


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