chown on a mounted NFS partition gives "Operation not permitted"

By default the root_squash export option is turned on, therefore NFS does not allow a root user from the client to perform operations as root on the server, instead mapping it to the user/group id specified by anonuid and anongid options (default=65534). This is configurable in /etc/exports together with other export options.

Read the section of the exports(5) concerning "root squashing":

Very often, it is not desirable that the root user on a client machine is also treated as root when accessing files on the NFS server. To this end, uid 0 is normally mapped to a different id: the so-called anony- mous or nobody uid. This mode of operation (called ‘root squashing’) is the default, and can be turned off with no_root_squash.

So you want:

/mnt/storage-pools   *(rw,insecure,sync,no_subtree_check,no_root_squash)

(edited typo)