An aggregate is composed of twelve 36-Gigabyte disks.

https://library.netapp.com/ecmdocs/ECMP1196986/html/GUID-8A91F6A2-61B8-42C3-AEAB7D5AA9BBE9CF.html

If a disk fails and no hot spare disk that exactly matches the failed disk is available, Data ONTAP uses the best available spare. Understanding how Data ONTAP chooses an appropriate spare when there is no matching spare enables you to optimize your spare allocation for your environment.

Data ONTAP picks a non-matching hot spare based on the following criteria (and more; in the link above):

If the available hot spares are not the correct size, Data ONTAP uses one that is the next size up, if there is one.

The replacement disk is downsized (aka right sized) to match the size of the disk it is replacing; the extra capacity is not available.