Uno Engborg wrote, On 05/07/2008 02:05 PM:
My idea is to run virtual machines that if hardware fails moves over to some
other physical box in case of a hardware failure. Even if you have fast
boxes with lots of memory, there is a limit to how many virtual machines
you can run on one box, and still get decent performance. So chances are
that I will nned more physical boxes. At the very least there should be a
plan on how to add them, and it should be possible to expand the system
without taking it down.
Most of the time, even though I have not ran any virtual machines under Linux
I would believe, that for each VM you have you'll have the VM running on one
machine and the other machine is just a backup.
So I think you could have a setup like the following with drbd of today:
RM=real machine
VM=virtual machine
(assuming you are running drbd at the RM level)
RM1
drbd0-3 shared with RM2 (VM0-3)
drbd4-7 shared with RM3 (VM4-7)
RM2
drbd0-3 shared with RM1
drbd4-7 shared with RM4 (VM8-11)
RM3
drbd0-3 shared with RM4 (VM12-15)
drbd4-7 shared with RM1
RM4
drbd0-3 shared with RM3
drbd4-7 shared with RM2
and normal running would have:
RM1 running VM0
RM1 running VM1
RM1 running VM4
RM1 running VM5
RM2 running VM2
RM2 running VM3
RM2 running VM8
RM2 running VM9
RM3 running VM6
RM3 running VM7
RM3 running VM12
RM3 running VM13
RM4 running VM10
RM4 running VM11
RM4 running VM14
RM4 running VM16
Then SOMEONE violently pulls the plug on RM2...
RM1 takes over running VM2 and VM3
RM4 takes over running VM8 and VM9
it is not fiendishly difficult to setup the DRBD configs, but heartbeat might
be a bit fun.
May I suggest taking this question over to
http://lists.linbit.com/mailman/listinfo/drbd-user
and asking there... I think I recall seeing traffic like this before there.
How long in the future? As soon as possible, or when I'm confident enough
to use this in a production environment.. By then I probably move to CentOS
RHEL, but I'm used to Fedora so I'll start testing
on that.
AFAIK DRBD should work as well on them as it does on fedora (modulus any old
kernel strangeness WRT drbd).
As you ask about the future, are there any new things on the horizon that I
should wait for?
I would not wait right now, because linbit has not given any ETA at all of
getting drbd+ functionality into the normal drbd[1], but getting to know drbd
and it's user list could help you plan.
[1] probably because they are too busy with trying to get a version of drbd
into the main Linus kernel tree.
2008/5/7 Todd Denniston <Todd.Denniston@xxxxxxxxxxxxxxxxxx>:
Uno Engborg wrote, On 05/07/2008 03:33 AM:
The problem is that it can't be expanded to more than 2 boxes in the
future.
what do you mean by more than 2 boxes[1], and how far in the future?
http://www.linbit.com/en/products-services/drbd/drbd-plus/
I believe they will probably roll this functionality into the openly
released version later, but even so they have described on the mailing list
that it's setup is very difficult, i.e., you'll want to pay them to set it
up.
[1] with the current setup you can have several nodes in one drbd cluster,
but _each_ drbd _resource_ is only mirrored between two nodes.
--
Todd Denniston
Crane Division, Naval Surface Warfare Center (NSWC Crane)
Harnessing the Power of Technology for the Warfighter
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