Hi Mark,
Thank you for detailed answer, but, actually, your vision is not
contradicted with mine, you just confirmed that the huge jump was made in
the last decade because of Linux on mainframe (in z/VM particularly).
I hope that with people like you, the speed of progress won't be slow
down.
WBR, Sergey
Mark Post <mp...@suse.com>
Sent by: Linux on 390 Port <LINUX-390@VM.MARIST.EDU>
28-09-15 23:39
Please respond to Linux on 390 Port
To: LINUX-390@VM.MARIST.EDU
cc:
Subject: Re: Documentation for Linux on z Systems and KVM -
new
>>> On 9/28/2015 at 02:25 AM, Sergey Korzhevsky <s_korzhev...@iba.by>
wrote:
> Alan Altmark wrote:
>>> What is it about z that makes virtualization work better?
>>50 years of work on it?
>
> That is interesting answer. One thing came to my mind is the live guest
> relocation. As far as i could find, VMware introduced that feature
> (vMotion) in 2003, z/VM - in 2011. The same regarding network
> (GuestLAN/VSwitch).
> So, looks like z/VM slept all that years and was wake up by x86 world
> recently.
Having been an active participant and observer of the community for a
while now, I think I can contribute some perspective. (From what I can
tell, you have been also so I find your comment a little surprising.)
When Linux for the mainframe was first introduced, a lot of facilities we
take for granted today didn't exist. Guest LANs, VSWITCHes, cooperative
memory management and so on. That started to change pretty quickly.
Things that actually helped running more than just a few instances of
Linux were introduced and made life much easier. Live Guest Relocation
wasn't needed then, because not many shops were running huge amounts of
guests. That pain came along later. Even then, it wasn't for the same
reason that the x86 world wanted it.
Mainframe shops running Linux on z/VM didn't worry much about hardware
failures and migrating workload to relieve overloaded servers usually
wasn't an issue because of decades of performance and capacity management.
What "we" wanted it for was because z/VM was so reliable it could run for
years but sometimes various maintenance was important to put on the
system. Trying to get multiple customers of the service to agree on a
maintenance window was becoming nearly impossible, because although they
wanted High Availability, they weren't willing to actually invest in it,
so the workload couldn't be failed over to another server in a cluster.
There was another factor, although not a technical one. Many customers
have become checklist driven. If your product doesn't allow them to put
check marks in all the boxes on the list, it's obviously not a good
product and not worthy of consideration. So, z/VM development was getting
reports from Sales that this function was needed, just to be "in the
game." And, being the group that they are, z/VM development wanted to
approach the development needed in a more "system of systems" oriented way
than just bolting on a feature. Thus, Single System Image was born, and
it took quite a while and a lot of people to bring to the market. Taking
into account the various diversions that were forced on them during the
same period of time, it's amazing they got it out as quickly as they did.
I think most people that have been in the z/VM world for a long time would
agree that having Linux available on the mainframe has breathed new life
into z/VM. Since then, they've been working hard to introduce things that
make sense for the mainframe environment. What new items they work on,
and what priority they have, _can_ be influenced by current and potential
customers. I encourage anyone who has thoughts on what those new items
should be to speak up, whether here or in the IBMVM mailing list, or at
SHARE. There are people in these mailing lists and at SHARE that have a
direct line into the z/VM and Linux development groups at IBM. Take
advantage of that.
Mark Post
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