Get device name used in pool:

zpool status nvmpool

# resize /dev/nvme0n1p3
parted /dev/nvme0n1

resizepart 3
End ? [X.XGB]?
quit

zpool online -e nvmpool nvme0n1p3

Shrinking of zpool is not possible, but trick with 2nd device (or even file) works:

• add 2nd device to zpool (can be smaller - only to fit data)
• remove 1st device - zpool will copy all data to another device.
• to create mirror, use attach not add

zpool list rpool -v
zpool offline rpool /dev/disk/by-id/SECOND-part3
zpool detach rpool /dev/disk/by-id/SECOND-part3

Resize /dev/disk/by-id/SECOND-part3 to smaller size.

zpool add rpool /dev/disk/by-id/SECOND-part3
zpool remove rpool /dev/disk/by-id/FIRST-part3

Sometimes ZFS refuse to remove device with 'out of space' error (but second device is capable to handle all data). To solve it, add more temporary devices to rpool

zfs create -V 64gb nvmpool/t1
zfs create -V 64gb nvmpool/t2
zpool add rpool /dev/zvol/nvmpool/t1
zpool add rpool /dev/zvol/nvmpool/t2

Resize /dev/disk/by-id/FIRST-part3 to smaller but equal to SECOND-part3 size.

zpool attach rpool /dev/disk/by-id/SECOND-part3 /dev/disk/by-id/FIRST-part3

zpool attach rpool /dev/dusk/by-id existing disk