DRS uses a cost benefit RISK approach to load balance a cluster. Before presenting the migration recommendations for a VM to load balance a cluster,

DRS calculates 3 things:

Cost: What will be the cost of migrating a VM from source to destination host? Cost here refers to the CPU and memory.

When a vMotion process in invoked on a VM, it reserves 30% of the cpu core (For 1 GB NIC) of that VM and 100% cpu core (For 10 GB NIC). This RESERVATION is created on both source and destination host. This reserves resources can’t be allocated to any other VM while vMotion is in progress. This can put some pressure on an Esxi host when it is heavily loaded.

Benefits: What will be the resource benefit that an Esxi host will get after migrating a virtual machine to other Esxi ho st. If after the migration CHLSD value of the Esxi host comes down then DRS will consider that migration as benefit.

Risk: Risk accounts for possibility of irregular loads. Suppose a VM has inconsistent and spiky demands of resources, then migrating such VM’s is not a good move because MAY be at the time of migration VM resource demand was LOW but after completion of migration, VM’s resource demands suddenly increased. In this case it can cause the increase in destination Esxi hosts CHLSD and again DRS has to perform migration of that VM to bring down CHLSD of the Esxi host where that VM was migrated.

DRS recommends migrations if Benefit obtained due to a migration < cost associated with that migration.

DRS uses a cost benefit risk approach to load balance a cluster. Before presenting the migration recommendations for a VM to load balance a cluster,

DRS calculates 3 things:

Cost: What will be the cost of migrating a VM from source to destination host? Cost here refers to the CPU and memory.

When a vMotion process in invoked on a VM, it reserves 30% of the cpu core (For 1 GB NIC) of that VM and 100% cpu core (For 10 GB NIC). This reservation is created on both source and destination host. This reserves resources can’t be allocated to any other VM while vMotion is in progress. This can put some pressure on an Esxi host when it is heavily loaded.

Benefits: What will be the resource benefit that an Esxi host will get after migrating a virtual machine to other Esxi ho st. If after the migration CHLSD value of the Esxi host comes down then DRS will consider that migration as benefit.

Risk: Risk accounts for possibility of irregular loads. Suppose a VM has inconsistent and spiky demands of resources, then migrating such VM’s is not a good move because may be at the time of migration VM resource demand was low but after completion of migration, VM’s resource demands suddenly increased. In this case it can cause the increase in destination Esxi hosts CHLSD and again DRS has to perform migration of that VM to bring down CHLSD of the Esxi host where that VM was migrated.

DRS recommends migrations if Benefit obtained due to a migration < cost associated with that migration.