45G of DOCKER_DISK_SIZE_GB creates only 40GB partition

probably the inode number is too high?

```
Filesystem                      1K-blocks      Used Available Use% Mounted on
/dev/sdb1                        41154912  36817680   1961604  95% /mnt/sdb1
```

```
Filesystem                       Size  Used Avail Use% Mounted on
/dev/sdb1                         40G   36G  1.9G  95% /mnt/sdb1
```