On Tue, Jun 7, 2016 at 3:08 PM, baby eklavya <baby.ekla...@gmail.com> wrote:
> Hi Listers ,
>
> To my understanding , when sharing MCS consoles in a sysplex , one thing
> which matters is the console name which has to be unique for each LPAR even
> though the UCB can be the same .
Then again , console uses EXCP to write
> the screen of data each time . Since the UCB is shared , how does it
> actually work ?
>
> Unlike DASD devices which goes via SSCH logic in which the device busy
> status is checked when applications from multiple LPARS try to write on the
> same UCB ,the console seems to be working in a different way in a sysplex .
>
The above is not strictly true, but the end result is similar.
>
> I have been searching on this for a while , but couldn't find anything
> documented about this so far . Can someone clarify /guide me where i can
> find this information ?
>
"the UCB can be the same" is not really true. A UCB is a software defined
data structure in a z/OS image's common memory. Each z/OS image has its
own, private, memory. So a UCB cannot be shared. There is no sharing of
memory between LPARs (well, that can be used as such by an OS). I don't
know what the actual I/O structures in the z hardware definitions are
called (i.e. those that are created by an POR from the IOCDS on the SE),
but I doubt it is a UCB (but I've been wrong before).
OTOH, A _device number_ is a "logical name" which is to be defined as 4
hexadecimal digits. Multiple LPARs can have identical _device number_,
which may (or may NOT) refer to the same (or different) devices. I.e.
device number 2000 may refer to a disk device in LPAR1 and LPAR2 can also
have a device number 2000 which refers to the same physical disk device
(common when sharing DASD). However, it is also possible to have a device
number, say, 1500 refer to a 3270 device in LPAR1. In LPAR2, device number
1500 can also be a 3270 device, but refer to a distinctly different
physical 3270 device. In this case, the CONSOLxx members in each z/OS image
can refer only to the device number 1500, but it will actually be for a
different physical device. In the CONSOLxx member of parmlib, each
console has a NAME (if you don't define it, is has a default of the device
number). In a SYSPLEX, the console __NAME__ must be unique across all
members of the SYSPLEX. But the device _number_ may be the same. I have
entries in CONSOLxx which look something like:
CONSOLE DEVNUM(5100) ROUTCODE(ALL)
PFKTAB(PFKTAB00)
AUTH(MASTER)
NAME(&SYSNAME.5100)
UNIT(3278-2)
MONITOR(JOBNAMES-T)
CON(N) SEG(20) DEL(R) RNUM(20) RTME(1) MFORM(J,T) AREA(NONE)
Each LPAR has a device number of 5100. However, device 5100 in each LPAR
is a __different__ physical 3270 device. I make the __NAME__ unique by
concatenating the z/OS sysname name, &SYSNAME, with the device number,
5100, so that the name of the consoles are things such as PROD5100 and
TEST5100 for the PROD and TEST z/OS images respectively. For simplicity,
the z/OS PROD system runs in the LPAR named PROD and the z/OS TEST system
runs in the LPAR named TEST.
> TIA ,
>
> Baby
>
--
The unfacts, did we have them, are too imprecisely few to warrant our
certitude.
Maranatha! <><
John McKown
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