When you expand a tdev, the meta member are not bound to the pool and during the expansion it is bound to the original pool. No pinning required.
Our environment is all virtually provisioned.  All metadevices are striped because we replicate almost everything.  We recently upgraded to 5875.198.148 and running SE 7.3.0.1 and have FAST VP moving data.  I ran a test to expand a striped meta using a thin BCV to protect the data and it worked just as advertised.  This device, however, was bound and completely allocated to the SATA pool.  My question is if I have a striped metadevice and need to expand it and it is under FAST VP control, which means it is spreading extents over multiple pools is that supported?   Is so, is it recommended that the device be pinned before doing the expansion?  Appreciate any thoughts... Chris
FAST VP and Striped Meta Expansion