Each instance and virtual machine comes with an allocated quantity of disk storage. Storage can be used either by directly attaching an onboard solid-state drive (SSD) or hard disk drive (HDD) to the virtual machine’s associated motherboard, or through volumes reserved on a separate storage-specific rack. Tailpipe distinguishes the former type as ‘onboard storage’, and the latter as ‘network storage’.
In AWS, onboard storage is delivered through the Simple Storage Service (S3). In Azure, it’s Blob Storage.
AWS network storage is called Elastic Block Storage (EBS). For Azure, it’s Azure Managed Disks.
Tailpipe measures onboard SSDs and HDDs separately to network SSDs and HDDs. There are two reasons for this:
- The two are measured on different bases. Cloud providers report the actual physical drives behind onboard storage, so Tailpipe can price each drive model from manufacturer datasheets. They do not do this for network storage, which is only reported as a volume in GB.
- This drives two different calculations. For onboard storage, Tailpipe generates a linear regression of power draws across drive models and capacities. Network storage is priced with per-GB coefficients derived from Lawrence Berkeley National Laboratory data center research, split by drive class. See Network Storage for more details.
To calculate onboard storage, Tailpipe first identifies whether an organization’s virtual machine utilizes onboard or network storage. If your virtual machine includes onboard storage, Tailpipe can then identify whether it is SSD or HDD storage from its virtual machine database.
Tailpipe models power consumption for onboard SSDs separately to onboard HDDs. This is because according to Tailpipe’s analysis of storage manufacturer’s datasheets, HDDs consume more power than SSDs. For SSDs, a dataset of 20 drives with capacities from 2TB to 15TB was analyzed. For HDDs, a dataset of 14 drives with capacities from 14TB to 24TB was analyzed. See Appendix B for details.
Solid State Drives
For onboard SSDs, power consumption is measured based on linear regressions of power draws for different drives at various capacities. This means Tailpipe can approximate the power draw of each different drive capacity (see Appendix C). Tailpipe can identify an organization’s drive capacity from the provider’s virtual machine specifications. For SSDs, Tailpipe also distinguishes between NVMe and SATA SSDs. NVMe SSDs have a significantly higher power consumption than SATA SSDs. Tailpipe can also ascertain which type of SSD is attached to a virtual machine based on cloud provider specifications. In AWS’ case, their specifications state when a virtual machine uses NVMe storage. It is assumed that the cheaper SATA SSDs are used if a virtual machine specification does not specify which SSD type it utilizes.
Power consumption for SSD storage is therefore calculated as follows:
NVMe SSD Power Consumption (W) = 0.0017 * GB of NVMe SSD Storage allocated
SATA SSD Power Consumption (W) = 0.00063 * GB of SATA SSD Storage allocated
Hard Disk Drives
For onboard HDDs, power consumption is calculated based on averaging of different power draws of HDDs at different capacities (see Appendix D):
Power consumption for HDD storage is therefore calculated as follows:
Onboard HDD Power Consumption (W) = 0.0022 * GB of HDD Storage allocated
Final Onboard Storage Calculation
Finally, the power consumption is multiplied by the length of the time the organization’s usage and billing file states the storage was used, to get an energy consumption figure:
Onboard Storage Energy Consumption (Wh) = Onboard Storage Power Consumption (W) * Number of Hours of Utilization