MSDB database stores all sql server agent related information. It contains all information about Jobs, Alerts, backup details, replication tables, log shipping tables, database maintenance plans and database mail details.
· The max size of ‘msdb’ log file is 2 TB. (SQL 2k5/2k8).
· This DB cannot be kept in Emergency mode.
· This DB cannot be removed directly from SSMS as we shouldn't not detach any of system DB’s directly. We have to do it from cmd prompt incase needed.