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List:       linux-390
Subject:    Re: about sharing filesystems
From:       John Summerfield <debian () herakles ! homelinux ! org>
Date:       2009-06-22 8:46:28
Message-ID: 4A3F44E4.8030304 () herakles ! homelinux ! org
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Richard Troth wrote:
> This started in the "To kick or to clone" thread.
>
>
> The z/VM crowd has a lot of experience with sharing filesystems.  Even
> now, with sophisticated handling of removable media, Linux is still a
> little rough.  What I mean is ... in Linux land we make way too little
> use of things like on-demand applications, programs which live on
> their own disk and are used when called for.  We're still thinking
> "RPM or bust", install it formally or it simply doesn't exist..
>
>
> In the VM/CMS world, everything always lives on its own disk.  You
> want the C compiler?  Link its disk and access it.  (Where in Linux
> speak that would be equiv to hot-plugging the media and mounting it.
> Please forgive me since most of you are well aware of the
> correlation.)  This is all the more elegant because you can, in the
> VM/CMS model, have multiple installations, multiple releases
> concurrently.  You can upgrade without interrupting active work.  The
> compiler is owned by a virtual machine called (perhaps) IBMC.


Linux isn't VM.

What does one do on the latest MVS and DOS/VS?

It's decades since I was a sysprog, but when I was we installed
compilers and the like on permanently-mounted DASD. Not a lot
differently from Linux, albeit very different in implementation.




>
>
> Maybe this is a good place to discuss Mike's idea?
>> An idea: In the first install of the golden image,
>> how about creating a small file system at /var/lib/rpm?
>> You maintain RPMs, and thus the RPM database,
>> on the golden image. When you create R/O clones,
>> they get a R/W /var/ file system of course - BUT! - the
>> golden image's /var/lib/rpm/ gets overmounted R/O.
>
>
> Sure.  This would work fine.
> And I see that Kyle Black reports some success with that.
>
>
> In my shop, we elected to retain a RW copy of the RPM DB
> because we can in fact still use RPM on the "clients"
> as long as the RPMs installed there do not step on RO space.
> For this to work, an  'rpm --justdb'  kind of reconciliation is needed
> when you upgrade the op sys.

I feel ill.
If your clones are forks of the Golden Master, that's one thing. If you
hope to share filesystems, you really need vendor support. Otherwise,
you will need to reinvent that particular wheel from time to time.




--

Cheers
John

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