RE: Quick AIX question rooted in a z/OS concept
- From: John.Mckown@xxxxxxxxxxxx (McKown, John)
- Date: 15 Jun 2007 10:55:33 -0700
-----Original Message-----
From: IBM Mainframe Discussion List
[mailto:IBM-MAIN@xxxxxxxxxxx] On Behalf Of Pommier, Rex R.
Sent: Friday, June 15, 2007 12:41 PM
To: IBM-MAIN@xxxxxxxxxxx
Subject: Quick AIX question rooted in a z/OS concept
Hi all.
I know this isn't a z/OS question but I don't think any of us
live in a
homogeneous environment and the best way I can think of
asking this AIX
question is to word it in z/OS terminology.
I have an application developer who wants to have 2 AIX LPARs access
shared disk. He thinks he can just have me point the LUN on
the SAN to
both LPARs and everything will work just fine. On my "Z", I
can set up
GRS or a third-party competitor to this to serialize I/O requests from
various LPARs/machines. Is there something in AIX that performs a
similar function? I asked this of an AIX list and the response I got
back was something called GPFS which they say can do this.
Unfortunately it appears as though I would need to buy and activate
HACMP to use GPFS. Is there something else, more of a stand-alone
product like GRS that would allow me to share a disk LUN
across multiple
AIX LPARs without having the LPARs step on each other?
Thanks and have a happy Friday.
Rex
You simply CANNOT DO THIS!! If you actually tried, you'd end up
scragging the UNIX filesystem. The only way to "share" data between UNIX
systems is via something like NFS (or GPFS or AFS or some other type of
thing).
This applies even in z/OS UNIX. If you create an HFS or zFS filesystem
and attempt to mount it on multiple z/OS systems which are not in the
same Parallel Sysplex with the appropriate setup, then you will "fry"
the UNIX filesystem. I've done it (by accident).
Trying to share a UNIX filesystem would be like trying to share a single
VSAM file in UPDATE mode between two different batch jobs on two
different z/OS images, and you didn't have RLS. There are some UNIX
filesystems (the aforementioned AFS or GPFS) which have something like
RLS so that filesystem information can be shared between the two UNIX
systems. UNIX buffers all the disk I/O into local caches. With two
separate UNIX systems, you have two separate caches and no
communications between them so that the caches remain coherent. Image
trying to run a multitask system with shared memory, but no "locking" or
other "safety precautions". You end up, eventually, with trash.
Bottom line: Not possible except with the aforementioned filesystems
such as AFS or GPFS. I am fairly sure the GPFS is an IBM filesystem for
AIX systems.
--
John McKown
Senior Systems Programmer
HealthMarkets
Keeping the Promise of Affordable Coverage
Administrative Services Group
Information Technology
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