Commit 3bc9b410 authored by Klaus Aehlig's avatar Klaus Aehlig

Design location: change weights for location to 1.0

In this way, we will be able to go through a temporarily unequal number
of disks on the nodes in order to satisfy location constraints.
Signed-off-by: default avatarKlaus Aehlig <aehlig@google.com>
Reviewed-by: default avatarPetr Pudlak <pudlak@google.com>
parent 091f4a8f
......@@ -54,13 +54,16 @@ The following components will be added cluster metric, weighed appropriately.
The weights for these components might have to be tuned as experience with these
setups grows, but as a starting point, both components will have a weight of
0.5 each. In this way, any common-failure violations are less important than
any hard constraints missed (instances on offline nodes, N+1 redundancy,
exclusion tags) so that the hard constraints will be restored first when
balancing a cluster. Nevertheless, with weight 0.5 the new common-failure
components will still be significantly more important than all the balancedness
components (cpu, disk, memory), as the latter are standard deviations of
fractions.
1.0 each. In this way, any common-failure violations are less important than
any hard constraints missed (like instances on offline nodes) so that
the hard constraints will be restored first when balancing a cluster.
Nevertheless, with weight 1.0 the new common-failure components will
still be significantly more important than all the balancedness components
(cpu, disk, memory), as the latter are standard deviations of fractions.
It will also dominate the disk load component which, which, when only taking
static information into account, essentially amounts to counting disks. In
this way, Ganeti will be willing to sacrifice equal numbers of disks on every
node in order to fulfill location requirements.
Appart from changing the balancedness metric, common-failure tags will
not have any other effect. In particular, as opposed to exclusion tags,
......
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