[Linux-HA] Don't start all groups at once?

[Andrew Beekhof]

On 10/2/07, Dejan Muhamedagic <dejanmm at fastmail.fm> wrote:
> Hi,
>
> On Mon, Oct 01, 2007 at 06:04:41PM -0700, Kelly Byrd wrote:
> > As I've mentioned before, I've got 22 groups, each of which is tied to one
> > of  22 master/slave drbd resources. During normal operation, one node runs
> > 11 and the other node runs the other 11.
> >
> > During a failure, 11 drbds their 11 groups will start on the remaining
> > node. This will be quite a load on the surviving machine and it's
> > currently running resources. Each group is a virtual machine trying to
> > allocate a few hundred megs of RAM and boot an OS. I'd like to space it
> > out a bit. Is this possible? I don't want to specify an strict ordering. I
> > don't actually care about the order and I don't want VM-14 to not come up
> > because VM-13 failed for some reason. Ideally, I could configure things so
> > heartbeat will start a few at a time, then wait a bit, then start a few
> > more. If that's not possible, then starting them all sequentially would be
> > fine, and I'll just put a delay in the group. I'm under the impression
> > that heartbeat will try and start all groups at the same time. Is this
> > true?
>
> Yes and no. One part, the CRM will want to have all started
> at once. However, the other one, the LRM doesn't run more
> than four resources at a time.

oh yeah, good point.  i'd forgotten about that part.

> If there are four currently
> running and some more runnable the latter are postponed for one
> second and then the queue checked again. This is, however, an
> undocumented feature, so it may change in the future. At any
> rate, we do try not to overwhelm the host. Note that the LRM has
> no notion of how "heavy" processes are. It would be interesting
> to see the results with this multitude of VMs as resources.
>
> To be on the safe side, as Andrew suggested, you should use
> various start-delay periods.
>
> Thanks,
>
> Dejan
>
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