On 2/19/07, Jan Vanbrabant <[EMAIL PROTECTED]> wrote:
But I would like to know precisely in what "blindfolded" & "less hostile environment" consists of.
The basic idea is that z/VM allows you to abstract from the actual hardware and presents an ideal machines to the operating system running in that virtual machine (to Linux, in this case). This is attractive because it allows the host to allocate real resources in the most suitable way without bothering the guest with the details. It also isolates the guest OS from specific hardware details because you only need the host to deal with those. Part of that ideal machine is for example that error recovery is kept outside the virtual machine where possible. Life with Linux ended up less ideal, for various reasons (mostly political, imho). We now find that z/VM reveals way to much details about the real system to the guest, and Linux code deals with those details as if it were running on bare metal. And everyone thinks that it is normal that you would need to upgrade all your Linux virtual machines just because you moved their mini disks from one DASD subsystem to the other.
You should know that besides z/OS, we are partially VM. But that platform is not strategic within our company. And after many years the management has finally decided to get rid of it and to migrate it to MVS. Should be realized by the 2-nd half of next year.
The other thing that z/VM provides is security and isolation. If you run your mainframe DASD shared among all LPARs, you should be aware that someone with root access on a Linux LPAR can (by accident) wipe out your z/OS production data. Something like that can kill a Proof of Concept project, if nothing more. Considering the lack of granularity in access control on Linux, you may find way too many people can do dangerous things. Especially when you connect that server to the ugly Internet. The virtual machine provided by z/VM restricts access to whatever that virtual machine needs to have (which may sometimes be even less than class G).
And now, zLinux is peeping around the corner ... with VM sitting & laughing on it's shoulder.
You're correct that Linux on the mainframe helped to keep VM around in many installations, has brought VM back in several shops, and caused new VM installations as well. That was intended, and it is good to see it worked out. I suppose that when you're looking at a very static situation with no future growth, then you might even get a business case for Linux on the mainframe without z/VM (like to replace a single 3745 and nothing more). In most situations however, the added value of z/VM is a key factor. And in your case the education issue probably does not apply, so you're just looking at license cost (and big egos of people who decided to get rid of z/VM) Rob ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
