By default, the entire capacity of the disk is reserved in advance. To create a growable disk that only allocates space that is actually used, add the following environment variable:
By default, the entire capacity of the disk is reserved in advance. To create a growable disk that only allocates space that is actually used, add the following environment variables:
```yaml
environment:
ALLOCATE: "N"
DISK_FMT: "qcow2"
```
This can also be used to convert any existing disks to the ```qcow2``` format.
This can also be used to convert your existing disks to the ```qcow2``` format.
Please note that disabling preallocation will negatively affect write performance any time the image needs to grow.
