As the number of servers installed in data centres continues to rise and its further increase is expected with the growth of AI and IoT systems going forward, there has been a demand for ways to increase server mounting density within the bounds of limited space and power.

Currently, the number of servers mounted to a data centre rack is limited by the total rated electrical power of the servers, which must be less than the power supply of the rack. However, server load is often times low—only at 10% to 50%—and power usage for each rack proportional to load is also low compared to the rated, resulting in low server mounting density.

To address this issue, Fujitsu Laboratories has developed a virtual machine (VM) control technology that enables efficient server placement by setting up a partition made up of backup servers in the data centre and migrating VMs to the backup partition based on the physical distribution and power consumption of the virtual machines.

The VM control algorithm first installs physical servers in racks at high density in a data centre and then establishes a back-up partition, using the migration functionality of the VMs to move them depending on the power consumption of each server. This way, it prevents each rack from exceeding its amount of power supply, according to Fujitsu.

Using an API that can be used in normal data centre management, the company will build a database related to the physical distribution, or the operational partition, of servers that provides services as well as the physical distribution of the backup partition that the VMs will be migrated to as it approaches its power supply limits.

Fujitsu_data-centre-VM_01 (cr) Figure 1: Increasing server mounting density in a data centre. (Source: Fujitsu)

Fujitsu_data-centre-VM_02 (cr) Figure 2: VM control technology based on physical distribution. (Source: Fujitsu)

Frequent migrations will occur if server mounting density is increased exceedingly, so an appropriate balance is necessary between migration frequency and server load commensurate with power volume. Fujitsu's VM control technology determines the number of servers that should be mounted on a rack by statistically estimating the frequency of migrations for each rack, based on the pre-measured load per server, assuming that changes in the load follow the normal distribution (Figure 3). If the centre of the normal distribution is a server load of 30%, for example, by installing servers based on a power usage value for 50% load, this would account for 95.5% of changes in load.

Fujitsu_data-centre-VM_03 (cr) Figure 3: Technology for setting rules for server installation. (Source: Fujitsu)

By using the newly developed technology, for example in a cloud service where changes in load can be predicted with a normal distribution, a data centre operating with 10 partitions at a server rack operating efficiency of 50% would be able to reduce space usage by 40%, with now five partitions and a server operating efficiency of 90%.

Fujitsu Laboratories plans to incorporate the technology into the Fujitsu Software ServerView Infrastructure Manager, Fujitsu Limited's infrastructure software for operations and management, within fiscal 2018.