Rick Troth wrote:
Virtualization of systems is about sharing of resources.
So think hard about sharing disks and not just memory and CPU.
On this point, cloning has a little edge. But both cloning and
jumpstarting (as usually implemented) suffer from difficulty
ferreting out the shared and sharable stuff from the per-system stuff.
But it can be done. Put the sharable stuff onto shared disks.
Got maint?
Apply your maint to the R/W copy, stamp out a new shared disk
from that copy, point the "client" systems to it, instant upgrade
of 500 servers without running 500 instances of RPM (or whatever).
There is always some per-system content
which must be either copied (clone) or deployed (kick).
The personalization of that per-system part is where jumpstart
has a little edge. Ideally, the personality would be retained
even if the rest of the op sys were blown away (er, uh, upgraded).
This is a little harder to do than sharing the op sys, but it can
be done. Start with the easy stuff, like user home directories.
There has been some discussion here before on sharing operating system
files/volumes.
A problem I see, have raised before, and not seen (or have forgotten) is
how to do it properly.
/ (root filesystem) can be shared, with some care.
/boot ditto
/usr can be shared without restriction
/etc contains per-host data, but it can be recreated by non-standard
means at IPL time. Care needs to be taken when changing its content, to
ensure the next IPL doesn't lose the changes.
/var contains per-system data that cannot be shared. Some of it (rpm
databases, yum/yast/you/whatever files) that reflect the contents of the
(shared) /usr and the (per-system) /etc.
For example
glibc - contains files in /usr, /etc and /. /var contains the rpm
database, so all have to be kept in step, unless you don't want to know
what is installed.
If I were your support supplier, I would not be keen on supporting this
in my standard contract.
--
Cheers
John
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