Moving the root volume from one aggregate to another is fairly straightforward. Be sure to be meticulous about each step. First, identify where the root volume is and what size it is. In this case our root volume is still the default name vol0.

toaster> vol container vol0
Volume 'vol0' is contained in aggregate 'aggr1'
toaster> vol size vol0
vol size: Flexible volume 'vol0' has size 14g.
toaster>

Create a new volume the same size (or larger) as vol0:

toaster> vol create root2 aggr2 14g
Creation of volume 'root2' with size 14g on containing aggregate
'aggr2' has completed.
toaster>

Now restrict the volume and use snapmirror to mirror the root volume to the new root volume you just created:

toaster> vol restrict root2
Volume 'root2' is now restricted.
snapmirror initialize -S vol0 root2
Transfer started.
Monitor progress with 'snapmirror status' or the snapmirror log.
toaster>
toaster> snapmirror status
Snapmirror is on.
Source                Destination           State          Lag        Status
toaster:vol0           toaster:root2          Uninitialized  -          Transferring  (150 MB done)

Once the transfer is complete, be paranoid and do one last update:

toaster> snapmirror status
Snapmirror is on.
Source                Destination           State          Lag        Status
toaster:vol0           toaster:root2          Snapmirrored   00:09:41   Idle
toaster>
toaster> snapmirror update -S vol0 root2
Transfer started.
Monitor progress with 'snapmirror status' or the snapmirror log.
toaster>
toaster> snapmirror status              
Snapmirror is on.
Source                Destination           State          Lag        Status
toaster:vol0           toaster:root2          Snapmirrored   00:00:12   Idle

Now break the snapmirror, making the destination new root volume writable:

toaster> snapmirror break root2
snapmirror break: Destination root2 is now writable.
Volume size is being retained for potential snapmirror resync.  If you would like to grow the volume and do not expect to resync, set vol option fs_size_fixed to off.
toaster>
toaster>

Mark the new root volume as ‘root’ using vol options:

toaster> vol options root2 root         
Wed Jul 31 09:36:06 PDT [toaster: fmmb.lock.disk.remove:info]: Disk 0a.32 removed from local mailbox set.
Wed Jul 31 09:36:07 PDT [toaster: fmmb.lock.disk.remove:info]: Disk 0c.16 removed from local mailbox set.
Wed Jul 31 09:36:08 PDT [toaster: fmmb.current.lock.disk:info]: Disk 2a.16 is a local HA mailbox disk.
Wed Jul 31 09:36:08 PDT [toaster: fmmb.current.lock.disk:info]: Disk 0c.48 is a local HA mailbox disk.
Volume 'root2' will become root at the next boot.
toaster>

Here you can reboot, or failover. If you need to keep the cluster up while performing this procedure, do a cf takeover from the other head in the cluster. Then when ready do a cf giveback to complete the reboot.

Now verify the root volume:

toaster> vol status
          vol0  online          raid_dp, flex     
          root2 online          raid_dp, flex     root, fs_size_fixed=on

As you can see root2 has the root option listed. Now offline the old root volume and destroy it:

toaster> vol offline vol0
Wed Jul 31 09:48:48 PDT [toaster: wafl.vvol.offline:info]: Volume 'vol0' has been set temporarily offline
Volume 'vol0' is now offline.
toaster> 
toaster> vol destroy vol0
Are you sure you want to destroy this volume? yes
Wed Jul 31 09:48:55 PDT [toaster: wafl.vvol.destroyed:info]: Volume vol0 destroyed.
Volume 'vol0' destroyed.
toaster> 
toaster> vol rename root2 vol0
'root2' renamed to 'vol0'
toaster> 

The migration is complete. Your new root volume is in a different aggregate, and the system is booted from it. The old one has been destroyed, and now you may destroy the old aggregate, or detach shelves, etc. Now check /etc/exports, and CIFS configuration. Since the new root is actually a copy you need to fix the NFS and CIFS configurations.