Primary storage overcommitment is used to control the available virtual primary storage space that can be allocated to VM instances. The calculation formula is as follows: Virtual primary storage space can be allocated = Physical primary storage space x Primary storage overcommitment ratio.
- Assume that the primary storage capacity is 2 TB. If the primary storage overcommitment ratio in the global settings is set to 2, the primary storage capacity is not changed after overcommitting. However, the primary storage capacity occupied by the volumes and snapshots is half of the actual capacity. For example, when you create a 100 GB volume (raw format), only 50 GB is occupied in the primary storage.
- Excessively large primary storage overcommitment ratio might seriously affect the storage pressure or cause the disk capacity to be fully occupied quickly and thus lead to system I/O errors. Therefore, primary storage overcommitting is not recommended. If you do need to perform primary storage overcommitting, make sure that the overcommitment ratio does not exceed 1.2.