Hello Dave,
from the cli help - note the clause "if not a VV set member"
Code:
OPTIONS
-ro
Specifies that if the specified virtual volume (<VV_name>) is a read-
write snapshot the snapshot's read-only parent volume is also updated
with a new snapshot [b][u]if the parent volume is not a member of a virtual
volume set. [/u][/b]If this option is not specified, the virtual volumes, as
indicated with the <VV_name> specifier, are replaced by a new snapshot.
See Notes for additional information.
Code:
After the updatevv command is executed, all VLUNs associated with the
specified virtual volume name are removed. The command then updates the
snapshots as follows:
If the -ro option is not specified, or if the specified virtual volume
name is a read-only snapshot, the command removes the snapshot, and
creates a new snapshot of the same name and of the same parent.
If the -ro option is specified and the specified virtual volume name is
a read-write snapshot, the virtual volume is removed and its read-only
parent is replaced by a new read-only snapshot of the same name. Then,
a new read-write snapshot is created of the new read-only snapshot. If
the read-only parent has multiple read-write snapshots, the updatevv
operation will fail because the read-only parent volume cannot be
removed.