Using Large I/O and Asynchronous Prefetch

Some dbcc commands can use large I/O and asynchronous prefetch if you configured these options for the caches that are used by the databases or objects to be checked.

dbcc checkdb and dbcc checktable use large I/O pools for the page chain checks on tables when the tables use a cache with large I/O configured. The largest available I/O size is used. When checking indexes, dbcc uses only 2K buffers.

The dbcc checkdb, dbcc checktable, and the dbcc allocation checking commands, checkalloc, tablealloc and indexalloc, use asynchronous prefetch when it is available for the pool in use. See Performance and Tuning Series: Query Processing and Abstract Plans > Setting Limits for dbcc.

Cache-binding commands and the commands to change the size and asynchronous prefetch percentages for pools are dynamic commands. If you use these dbcc commands during off-peak periods, when user applications experience little impact, you can change these settings to speed dbcc performance and restore the normal settings when dbcc checks are finished.