Long delay before redirected restore "starts"
Between the RESTORE DATABASE ... REDIRECT and the RESTORE DATABASE ... CONTINUE command, you will execute all of the SET TABLESPACE CONTAINER commands.

If your database resides on a filesystem that does not support fast file allocation (for example: AIX JFS2), then these SET TABLESPACE CONTAINER operations can take quite a long time if you have large containers – DB2 is formatting the tablespace containers.

When this is happening you'll see lots of I/O on your system, but no apparent activity on the database restore.