What is the difference between OFFLINE and ONLINE index rebuild in SQL Server?

Question

When rebuilding an index, there is an option for ONLINE=OFF and ONLINE=ON. I know that when ONLINE mode is on, it makes a copy of the index, switches new queries to utilizing it

Answer 1

The main differences are:

1) OFFLINE index rebuild is faster than ONLINE rebuild.

2) Extra disk space required during SQL Server online index rebuilds.

3) SQL Server locks acquired with SQL Server online index rebuilds.

• This schema modification lock blocks all other concurrent access to the table, but it is only held for a very short period of time while the old index is dropped and the statistics updated.