Q

What changes are required to convert an LPAR to native zLinux?

We have two z800 machines containing five LPARs -- three productions and two test environments. We are looking into converting one of the test LPARs to a native zLinux. Since the DASD of the test LPARs is separated from production ones, there is no need to be worried about the DASD on that environment.

The question is: Do we need to change anything on the IOCDS to reflect zLinux (native, not under z/VM), taking into consideration that we will utilize all available DASD on the test environment? Are there any hardware changes needed (e.g., adding Linux processor and the changes on the HMC profile)?

We have two z800 machines containing five LPARs -- three productions and two test environments. We are looking into converting one of the test LPARs to a native zLinux. Since the DASD of the test LPARs is separated from production ones, there is no need to be worried about the DASD on that environment.

The question is: Do we need to change anything on the IOCDS to reflect zLinux (native, not under z/VM), taking

into consideration that we will utilize all available DASD on the test environment? Are there any hardware changes needed (e.g., adding Linux processor and the changes on the HMC profile)?

No, there are no changes that are required, although best practice dictates you should allow a Linux system running in an LPAR to see only the devices that are absolutely necessary for it to access (counter to the practice of having everything visible to every LPAR that is common in the z/OS world). Extra devices defined in a LPAR will cause Linux IPL to be extremely slow -- this includes network devices, terminals, etc. -- as the Linux kernel must sense and identify every device defined to the LPAR, which can take a very long time (10 minutes or more) in a large configuration. Linux LPARs should be permitted to see only what they are allowed to use right now.

With regard to the HMC, the only change you should need to do to the HMC profiles is to ensure that the LPAR IPLs from the correct volume when activated.

That said, I'll strongly encourage you to get z/VM ASAP unless you are in one of the very few scenarios where running in LPAR makes sense (see one of my earlier responses for why and when Linux in LPAR mode is useful). The time and effort you'll spend solving the system management headaches for LPAR operations are more than enough to justify the cost of z/VM several times over.

This was first published in December 2005

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