Information Technology Reference
In-Depth Information
recommendations need manual approval, but the recommendation is not noticed (or an admin-
istrator is not even in the ofi ce). An hour later, the VMs that caused the recommendation in the
i rst place have settled down and are now operating normally. At this point, the DRS tab no lon-
ger rel ects the recommendation. The recommendation has since been withdrawn. If the migra-
tion were still listed, an administrator might approve it and cause an imbalance where one did
not exist.
In many cases, priority 1 recommendations have little to do with load on the cluster. Instead,
priority 1 recommendations are generally the result of one of two conditions. The i rst condi-
tion that causes a priority 1 recommendation is when you put a host into maintenance mode, as
shown in Figure 12.21.
Figure 12.21
An ESXi host put
into maintenance
mode cannot power
on new VMs or be a
target for vMotion.
Maintenance mode is a host setting that prevents the ESXi host from performing any
VM-related functions. VMs running on a host being put into maintenance mode must be shut
down or moved to another host before the host will actually enter maintenance mode. That is,
an ESXi host in a DRS-enabled cluster will automatically generate priority 1 recommendations
to migrate all VMs to other hosts within the cluster. Figure 12.20 shows priority 1 recommenda-
tions generated as the result of an ESXi host being placed into maintenance mode.
The second condition that could cause a priority 1 recommendation is when DRS afi nity
rules come into play. This leads us to a discussion of DRS afi nity rules.
