Have a look at the redbook "Getting started with ADSM: A practical
implementation guide",
SG24-5416.
They recommend to define separate storage pools for client directory
information and client data.
The storage pool for client directory information is located on disk and
large enough to hold all
directory data. Migration is turned off so you always restore directly from
disk (see page 89).

"You can use this option to make your restores quicker by keeping your
directory data on a
primary disk storage pool instead of on tape. The directory information is
the first
thing that is rebuilt during a restore and by making it quickly accessible,
your
restore time will be improved." page 111 or see page 242 (DIRMC).

Hope this helps

Kind regards
Thomas Rupp
Vorarlberger Illwerke AG
MAIL:   thomas.rupp AT illwerke DOT at
TEL:    ++43/5574/4991-251
FAX:    ++43/5574/4991-820-8251