🚀 go-pugleaf

On Wed, 12 Jul 89 12:59:00 PDT Michael Stein said:
>   As an MVS person, I always thought this was a VM list, but
>   since I haven't received even one response so far I've decided
>   it's just a CMS list...  Anyone have any information on this?
>   (last chance on this list).
>
No need to be nasty.  People usually wait a little bit to see if someone
more (read truely) knowledgable responds to the mail first.
>               - - -
>
>All these questions are about CP's DASD Block I/O System Service.
>
>1. Can multiple Virtual Machines use this service in multi-write
>   mode on the same disk at the same time?  I am assuming that
>   these VM's are responsible for the interlocking, I just want
>   CP to get the I/O done.  (It's not a CMS format disk).
Access to these minidisks is controlled by CP, so the MW access mode
of the CP LINK command should allow you to do that with little trouble.

>
>2. Can I use the whole disk (offset = 0)?
You can use the entire area of the file created by the CMS RESERVE command
(discussed under item 4.).  The volume label and other system areas on the
minidisk (IPL blocks, allocation blocks, pointer blocks) will not be
available through the *BLOCKIO system service.

>
>3. Can I use negative block numbers if the offset isn't zero?
no.

>
>4. How do I initially format the mini-disk? (CKD/FBA)?
>   (This doesn't have to be fancy.  Filling it with 4k blocks
>    would be fine as long as all the blocks are there).
The initial format of the disk is done with the standard CMS FORMAT command.
You can specify and of the normal EDF blocksizes (512, 1K, 2K, 4K).  You
cannot use the old CDF compatibility blksize of 800.  A file with mode 6
is created in the usable area of the minidisk by the CMS RESERVE command.
It is the RESERVE command that does not support a blksize of 800.

>
>5. Is there a non-standard length block near the begining of
>   the mini-disk (like a volume label at record 3?)
Keep in mind that this is a CMS minidisk.  It just has one file on it.  Like
any other CMS minidisk it has the volume (CMS1) record at block or physical
record 3.  The length of that record will be the blksize that was used
(explicitly or by default) in the FORMAT command.


One more thing:
The *BLOCKIO system service is an IUCV connected service.  Each disk you
are using *BLOCKIO with requires an IUCV connection.  If you are communicating
with another VM via IUCV then that will also take up an IUCV path.  By default
there are only four such paths per VM.  If you plan to have more then you
will need to code an "OPTION MAXCONN ????" in the directory entry of each
VM requiring more than four paths.

Smooth sailing!

Tim DiLauro     (301)955-4770      Systems Programmer
Johns Hopkins University School of Hygiene and Public Health