I believe that index reorg will use the tablespace that contains the index(es).
Here's what I dug out from the DB2 Admin Performance Guide -
REORG INDEXES has the following requirements:
- SYSADM, SYSMAINT, SYSCTRL or DBADM authority, or CONTROL privilege on the indexes and table
- An amount of free space in the table space where the indexes are stored equal to the current size of the index
Consider placing indexes subject to reorganization in a large table space when you issue the CREATE TABLE statement.
- Additional log space REORG INDEXES logs its activity. As a result, the reorganization might fail, especially if the system is busy and other concurrent activity is logged.
Note: If a REORG INDEXES ALL with the ALLOW NO ACCESS option fails, the indexes are marked bad and the operation is not undone. However, if a REORG with the ALLOW READ ACCESS or a REORG with the ALLOW WRITE ACCESS option fails, the original index object is restored.
HTH
-- Jayesh