Transaction Log space for DBCC DBREINDEX

1.The log space required by DBCC DBREINDEX is roughly equivalent to the number of index pages multiplied by 8 KB.

2. You can use DBCC SHOWCONTIG to determine the number of pages in a given index

3.When in full recovery mode, DBCC DBREINDEX logs images of each index page


Diff between DBReindex and DBCC Showcontig
http://www.microsoft.com/technet/prodtechnol/sql/2000/maintain/ss2kidbp.mspx#EFAA