Are there any issues that may affect Top Secret when migrating to a DS8886 DASD?
There are not any hardware dependencies, so there is no special consideration.
Top Secret can not currently exploit the EAV (Extended Access Volumes) functionality for the Top Secret files (security, backup, recovery).
With Top Secret fixes LU00423 and LU02579 applied, the AUDIT/TRACKING file allocation allows EAV and DSNTYPE=LARGE.