Issue : When running DBCC CHECKDB on SQL server 2000, We are facing t-log growth & blocking.

Cause : DBCC CHECKDB does block in 2000 and earlier. The code for DBCC in 2000 was complex since it was working against a moving target (the database being modified), so to have a consistent database to check, DBCC used the transaction log to keep track of what modifications was performed while DBCC was running. Due to this blocking cause.

DBCC CHECKDB was completely re-written in 2005. It now uses a database snapshot, hence no need to block. Thanks to Pual & Team.