RE: Quick AIX question rooted in a z/OS concept

John,

Thanks for the info. I know I need something like GPFS to do this. I'm
NOT going to allow the programmer to just hope for the best and share
the disk. What I was looking for was something akin to GPFS (hopefully
without the admin overhead of HACMP) that would allow me to do this
safely. GPFS is definitely an IBM product. Can you tell me what AFS
is? NFS won't work for me because that is giving me a single point of
failure in that if the NFS server goes down, I've lost access to the
data from both sides of the AIX LPARs.

Rex

-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-MAIN@xxxxxxxxxxxx
Behalf Of McKown, John
Sent: Friday, June 15, 2007 12:55 PM
To: IBM-MAIN@xxxxxxxxxxx
Subject: Re: Quick AIX question rooted in a z/OS concept

-----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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